feat(tools): Add Spectral Brush Editor UI (Phase 2 of Task #5)

Implement web-based editor for procedural audio tracing.

New Files:
- tools/spectral_editor/index.html - Main UI structure
- tools/spectral_editor/style.css - VSCode-inspired dark theme
- tools/spectral_editor/script.js - Editor logic (~1200 lines)
- tools/spectral_editor/dct.js - IDCT/DCT implementation (reused)
- tools/spectral_editor/README.md - Complete user guide

Features:
- Dual-layer canvas (reference + procedural spectrograms)
- Bezier curve editor (click to place, drag to adjust, right-click to delete)
- Profile controls (Gaussian sigma slider)
- Real-time audio playback (Key 1=procedural, Key 2=original, Space=stop)
- Undo/Redo system (50-action history with snapshots)
- File I/O:
  - Load .wav/.spec files (FFT/STFT or binary parser)
  - Save procedural_params.txt (human-readable, re-editable)
  - Generate C++ code (copy-paste ready for runtime)
- Keyboard shortcuts (Ctrl+Z/Shift+Z, Ctrl+S/Shift+S, Ctrl+O, ?)
- Help modal with shortcut reference

Technical:
- Pure HTML/CSS/JS (no dependencies)
- Web Audio API for playback (32 kHz sample rate)
- Canvas 2D for visualization (log-scale frequency)
- Linear Bezier interpolation matching C++ runtime
- IDCT with overlap-add synthesis

Next: Phase 3 (currently integrated in Phase 2)
- File loading already implemented
- Export already implemented
- Ready for user testing!

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 459 insertions, 0 deletions

diff --git a/tools/spectral_editor/style.css b/tools/spectral_editor/style.css
new file mode 100644
index 0000000..36b4eb3
--- /dev/null
+++ b/tools/spectral_editor/style.css
@@ -0,0 +1,459 @@
+/* Spectral Brush Editor Styles */
+
+* {
+    margin: 0;
+    padding: 0;
+    box-sizing: border-box;
+}
+
+body {
+    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
+    background: #1e1e1e;
+    color: #d4d4d4;
+    overflow: hidden;
+    height: 100vh;
+}
+
+#app {
+    display: flex;
+    flex-direction: column;
+    height: 100vh;
+}
+
+/* Header */
+header {
+    background: #252526;
+    padding: 12px 20px;
+    border-bottom: 1px solid #3e3e42;
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+}
+
+header h1 {
+    font-size: 18px;
+    font-weight: 600;
+    color: #cccccc;
+}
+
+.header-controls {
+    display: flex;
+    align-items: center;
+    gap: 15px;
+}
+
+.file-info {
+    font-size: 13px;
+    color: #858585;
+}
+
+/* Main content area */
+.main-content {
+    display: flex;
+    flex: 1;
+    overflow: hidden;
+}
+
+/* Canvas container (80% width) */
+.canvas-container {
+    flex: 1;
+    position: relative;
+    background: #1e1e1e;
+    border-right: 1px solid #3e3e42;
+}
+
+#spectrogramCanvas {
+    width: 100%;
+    height: 100%;
+    display: block;
+    cursor: crosshair;
+}
+
+.canvas-overlay {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    display: flex;
+    flex-direction: column;
+    justify-content: center;
+    align-items: center;
+    background: rgba(30, 30, 30, 0.9);
+    pointer-events: none;
+}
+
+.canvas-overlay.hidden {
+    display: none;
+}
+
+.canvas-overlay p {
+    font-size: 16px;
+    margin: 8px 0;
+}
+
+.canvas-overlay .hint {
+    font-size: 13px;
+    color: #858585;
+}
+
+/* Toolbar (20% width) */
+.toolbar {
+    width: 250px;
+    background: #252526;
+    padding: 15px;
+    display: flex;
+    flex-direction: column;
+    gap: 10px;
+    overflow-y: auto;
+}
+
+.toolbar h3 {
+    font-size: 14px;
+    font-weight: 600;
+    color: #cccccc;
+    margin-bottom: 5px;
+}
+
+.btn-toolbar {
+    padding: 8px 12px;
+    background: #0e639c;
+    color: white;
+    border: none;
+    border-radius: 3px;
+    cursor: pointer;
+    font-size: 13px;
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    transition: background 0.2s;
+}
+
+.btn-toolbar:hover {
+    background: #1177bb;
+}
+
+.btn-toolbar:disabled {
+    background: #3e3e42;
+    color: #858585;
+    cursor: not-allowed;
+}
+
+.btn-toolbar.btn-danger {
+    background: #a82d2d;
+}
+
+.btn-toolbar.btn-danger:hover:not(:disabled) {
+    background: #c94242;
+}
+
+.curve-list {
+    margin-top: 10px;
+    display: flex;
+    flex-direction: column;
+    gap: 5px;
+}
+
+.curve-item {
+    padding: 8px 10px;
+    background: #2d2d30;
+    border-radius: 3px;
+    cursor: pointer;
+    font-size: 13px;
+    transition: background 0.2s;
+    border: 1px solid transparent;
+}
+
+.curve-item:hover {
+    background: #3e3e42;
+}
+
+.curve-item.selected {
+    background: #094771;
+    border-color: #0e639c;
+}
+
+/* Control panel (bottom) */
+.control-panel {
+    background: #252526;
+    border-top: 1px solid #3e3e42;
+    padding: 12px 20px;
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    gap: 20px;
+}
+
+.control-section {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+}
+
+.control-section label {
+    font-size: 13px;
+    color: #cccccc;
+    white-space: nowrap;
+}
+
+.select-input {
+    padding: 4px 8px;
+    background: #3c3c3c;
+    color: #cccccc;
+    border: 1px solid #3e3e42;
+    border-radius: 3px;
+    font-size: 13px;
+    cursor: pointer;
+}
+
+.slider {
+    width: 150px;
+    height: 4px;
+    -webkit-appearance: none;
+    appearance: none;
+    background: #3e3e42;
+    border-radius: 2px;
+    outline: none;
+}
+
+.slider::-webkit-slider-thumb {
+    -webkit-appearance: none;
+    appearance: none;
+    width: 14px;
+    height: 14px;
+    background: #0e639c;
+    border-radius: 50%;
+    cursor: pointer;
+}
+
+.slider::-moz-range-thumb {
+    width: 14px;
+    height: 14px;
+    background: #0e639c;
+    border-radius: 50%;
+    cursor: pointer;
+    border: none;
+}
+
+.number-input {
+    width: 60px;
+    padding: 4px 6px;
+    background: #3c3c3c;
+    color: #cccccc;
+    border: 1px solid #3e3e42;
+    border-radius: 3px;
+    font-size: 13px;
+}
+
+.playback-controls {
+    gap: 8px;
+}
+
+.btn-playback {
+    padding: 6px 12px;
+    background: #0e639c;
+    color: white;
+    border: none;
+    border-radius: 3px;
+    cursor: pointer;
+    font-size: 12px;
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    transition: background 0.2s;
+}
+
+.btn-playback:hover:not(:disabled) {
+    background: #1177bb;
+}
+
+.btn-playback:disabled {
+    background: #3e3e42;
+    color: #858585;
+    cursor: not-allowed;
+}
+
+.btn-playback kbd {
+    background: rgba(255, 255, 255, 0.1);
+    padding: 2px 5px;
+    border-radius: 3px;
+    font-size: 11px;
+}
+
+/* Action bar (bottom) */
+.action-bar {
+    background: #2d2d30;
+    border-top: 1px solid #3e3e42;
+    padding: 10px 20px;
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+}
+
+.action-group {
+    display: flex;
+    gap: 8px;
+}
+
+.btn-action {
+    padding: 6px 12px;
+    background: #3c3c3c;
+    color: #cccccc;
+    border: 1px solid #3e3e42;
+    border-radius: 3px;
+    cursor: pointer;
+    font-size: 12px;
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    transition: background 0.2s, border-color 0.2s;
+}
+
+.btn-action:hover:not(:disabled) {
+    background: #505050;
+    border-color: #0e639c;
+}
+
+.btn-action:disabled {
+    color: #858585;
+    cursor: not-allowed;
+}
+
+.btn-primary {
+    padding: 6px 16px;
+    background: #0e639c;
+    color: white;
+    border: none;
+    border-radius: 3px;
+    cursor: pointer;
+    font-size: 13px;
+    transition: background 0.2s;
+}
+
+.btn-primary:hover {
+    background: #1177bb;
+}
+
+/* Icon styling */
+.icon {
+    font-size: 14px;
+    line-height: 1;
+}
+
+/* Modal */
+.modal {
+    position: fixed;
+    z-index: 1000;
+    left: 0;
+    top: 0;
+    width: 100%;
+    height: 100%;
+    background-color: rgba(0, 0, 0, 0.7);
+    display: flex;
+    justify-content: center;
+    align-items: center;
+}
+
+.modal-content {
+    background-color: #252526;
+    padding: 30px;
+    border: 1px solid #3e3e42;
+    border-radius: 5px;
+    width: 600px;
+    max-height: 80vh;
+    overflow-y: auto;
+    position: relative;
+}
+
+.modal-close {
+    position: absolute;
+    right: 15px;
+    top: 15px;
+    font-size: 28px;
+    font-weight: bold;
+    color: #858585;
+    cursor: pointer;
+    line-height: 1;
+}
+
+.modal-close:hover {
+    color: #cccccc;
+}
+
+.modal-content h2 {
+    font-size: 20px;
+    margin-bottom: 20px;
+    color: #cccccc;
+}
+
+.modal-content h3 {
+    font-size: 16px;
+    margin-top: 20px;
+    margin-bottom: 10px;
+    color: #cccccc;
+}
+
+.shortcuts-table {
+    width: 100%;
+    border-collapse: collapse;
+    margin-bottom: 20px;
+}
+
+.shortcuts-table th,
+.shortcuts-table td {
+    padding: 8px 12px;
+    text-align: left;
+    border-bottom: 1px solid #3e3e42;
+}
+
+.shortcuts-table th {
+    background: #2d2d30;
+    font-weight: 600;
+    color: #cccccc;
+}
+
+.shortcuts-table td {
+    color: #d4d4d4;
+}
+
+.shortcuts-table kbd {
+    background: #3c3c3c;
+    border: 1px solid #3e3e42;
+    padding: 3px 8px;
+    border-radius: 3px;
+    font-family: monospace;
+    font-size: 12px;
+}
+
+.modal-content ul {
+    list-style: none;
+    padding-left: 0;
+}
+
+.modal-content li {
+    padding: 5px 0;
+    color: #d4d4d4;
+}
+
+.modal-content li strong {
+    color: #cccccc;
+}
+
+/* Scrollbar styling */
+::-webkit-scrollbar {
+    width: 10px;
+    height: 10px;
+}
+
+::-webkit-scrollbar-track {
+    background: #1e1e1e;
+}
+
+::-webkit-scrollbar-thumb {
+    background: #3e3e42;
+    border-radius: 5px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+    background: #4e4e52;
+}