Update docs, fix Pygame window, and improve camera stage timing

AGENTS.md

@@ -12,7 +12,7 @@ This project uses:
 
 ```bash
 mise run install          # Install dependencies
-# Or: uv sync --all-extras   # includes mic, websocket, sixel support
+# Or: uv sync --all-extras   # includes mic, websocket support
 ```
 
 ### Available Commands
@@ -206,20 +206,6 @@ class TestEventBusSubscribe:
 
 **Never** modify a test to make it pass without understanding why it failed.
 
-## Architecture Overview
-
-- **Pipeline**: source → render → effects → display
-- **EffectPlugin**: ABC with `process()` and `configure()` methods
-- **Display backends**: terminal, websocket, sixel, null (for testing)
-- **EventBus**: thread-safe pub/sub messaging
-- **Presets**: TOML format in `engine/presets.toml`
-
-Key files:
-- `engine/pipeline/core.py` - Stage base class
-- `engine/effects/types.py` - EffectPlugin ABC and dataclasses
-- `engine/display/backends/` - Display backend implementations
-- `engine/eventbus.py` - Thread-safe event system
-=======
 ## Testing
 
 Tests live in `tests/` and follow the pattern `test_*.py`.
@@ -336,9 +322,9 @@ Functions:
 - **Display abstraction** (`engine/display/`): swap display backends via the Display protocol
   - `display/backends/terminal.py` - ANSI terminal output
   - `display/backends/websocket.py` - broadcasts to web clients via WebSocket
-  - `display/backends/sixel.py` - renders to Sixel graphics (pure Python, no C dependency)
   - `display/backends/null.py` - headless display for testing
   - `display/backends/multi.py` - forwards to multiple displays simultaneously
+  - `display/backends/moderngl.py` - GPU-accelerated OpenGL rendering (optional)
   - `display/__init__.py` - DisplayRegistry for backend discovery
 
 - **WebSocket display** (`engine/display/backends/websocket.py`): real-time frame broadcasting to web browsers
@@ -349,8 +335,7 @@ Functions:
 - **Display modes** (`--display` flag):
   - `terminal` - Default ANSI terminal output
   - `websocket` - Web browser display (requires websockets package)
-  - `sixel` - Sixel graphics in supported terminals (iTerm2, mintty, etc.)
-  - `both` - Terminal + WebSocket simultaneously
+  - `moderngl` - GPU-accelerated rendering (requires moderngl package)
 
 ### Effect Plugin System