docs: Streamline headless mode documentation

Summary:
- HEADLESS_MODE.md: 58→32 lines (-45%)
- HOWTO.md: Condensed to one-liner + reference
- Removed implementation details (in code comments)
- Simplified comparison table
- Clearer use case description

handoff(Claude): Documentation cleanup

2 files changed, 13 insertions, 45 deletions

diff --git a/doc/HEADLESS_MODE.md b/doc/HEADLESS_MODE.md
index 35098b1..2365906 100644
--- a/doc/HEADLESS_MODE.md
+++ b/doc/HEADLESS_MODE.md
@@ -1,33 +1,17 @@
-// Headless Mode Documentation
+// Headless Mode - Testing without GPU
 // Workspace: demo (shared across all workspaces)
 
 # Headless Mode
 
-Minimal GPU/platform stubs for testing without graphics.
+Run audio/timeline without GPU overhead. Useful for CI, audio dev, fast iteration.
 
-## Use Cases
-
-- CI/CD without GPU
-- Audio/tracker iteration
-- Timeline validation
-- Fast testing cycles
-
-## Build
+## Build & Run
 
 ```bash
 cmake -B build_headless -DDEMO_HEADLESS=ON
 cmake --build build_headless -j4
-```
-
-Or use the test script:
-```bash
-./scripts/test_headless.sh
-```
 
-## Usage
-
-```bash
-# 30s simulation (default)
+# 30s simulation (default, progress every 5s)
 ./build_headless/demo64k --headless
 
 # Custom duration
@@ -37,22 +21,12 @@ Or use the test script:
 ./build_headless/demo64k --dump_wav test.wav
 ```
 
-Progress printed every 5s.
-
-## Implementation
-
-- **GPU stub:** Validates lifecycle, maintains MainSequence
-- **Platform stub:** Simulates 60Hz time progression
-- **Main loop:** Audio updates without rendering
+Test script: `./scripts/test_headless.sh`
 
 ## vs STRIP_EXTERNAL_LIBS
 
-| Feature | HEADLESS | STRIP_EXTERNAL_LIBS |
-|---------|----------|---------------------|
-| Compiles | Yes | Yes |
-| Runs | Yes | No |
-| Audio | Full | No-op |
-| Timeline | Full | No |
-| Tests | Pass | Fail |
-
-See `src/gpu/headless_gpu.cc` and `src/platform/headless_platform.cc` for details.
+| | HEADLESS | STRIP_EXTERNAL_LIBS |
+|---|---|---|
+| **Runs** | ✓ | ✗ |
+| **Audio/Timeline** | ✓ Full | ✗ No-op |
+| **Purpose** | Testing | Size measurement |
diff --git a/doc/HOWTO.md b/doc/HOWTO.md
index fccfa1e..cafcf4a 100644
--- a/doc/HOWTO.md
+++ b/doc/HOWTO.md
@@ -47,16 +47,10 @@ cmake --build build -j4
 
 ### Headless Testing
 ```bash
-# Build without GPU
-cmake -B build_headless -DDEMO_HEADLESS=ON
-cmake --build build_headless -j4
-
-# Run simulation (30s default)
-./build_headless/demo64k --headless
-
-# Custom duration
-./build_headless/demo64k --headless --duration 60
+cmake -B build_headless -DDEMO_HEADLESS=ON && cmake --build build_headless -j4
+./build_headless/demo64k --headless --duration 30
 ```
+See `doc/HEADLESS_MODE.md`.
 
 ### Size Measurement
 ```bash