docs: Condense HOWTO.md, move details to technical docs

- HOWTO.md: 184→97 lines (quick reference only)
- BUILD.md: Add build modes, header organization, dependency tracking
- ASSET_SYSTEM.md: Add developer workflow section
- TRACKER.md: Add AudioEngine API documentation

Net: -147 lines in HOWTO.md

1 files changed, 39 insertions, 0 deletions

diff --git a/doc/TRACKER.md b/doc/TRACKER.md
index 6e71951..48829c0 100644
--- a/doc/TRACKER.md
+++ b/doc/TRACKER.md
@@ -74,3 +74,42 @@ PATTERN short_fill LENGTH 0.5   # 2 beats = 1 second at 120 BPM
 
 Potential runtime modifiers (not yet implemented):
 - Randomization, accents, volume modulation, distortion, noise, effects
+
+---
+
+## AudioEngine API
+
+**Production usage:**
+```cpp
+#include "audio/audio_engine.h"
+
+audio_init();
+static AudioEngine g_audio_engine;
+g_audio_engine.init();
+
+// Main loop
+g_audio_engine.update(music_time);
+
+g_audio_engine.shutdown();
+audio_shutdown();
+```
+
+**Methods:**
+- `init()`: Initialize synth + tracker
+- `update(music_time)`: Update music state, trigger patterns
+- `shutdown()`: Cleanup
+- `seek(time)`: Jump to timestamp (debug builds only)
+
+**Testing:**
+```cpp
+AudioEngine engine;
+engine.init();
+engine.update(1.0f);
+engine.shutdown();
+```
+
+**Direct synth APIs** (performance-critical code only):
+- `synth_register_spectrogram()`
+- `synth_trigger_voice()`
+- `synth_get_output_peak()`
+- `synth_render()`