Move all animations to Pico firmware, Pi becomes HTTP-serial bridge

Pico runs all 9 mood animations and jaw modes locally instead of
receiving per-LED serial commands from the Pi. New protocol: bare
integers for fire-and-forget jaw amplitude, "mood X" / "jaw X" for
mode switches. Cuts light_service.py from 409 to 193 lines.

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

docs/plans/2026-01-31-pico-side-animations-design.md

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+# Pico-Side Animations - Phase 1
+
+Move all animation logic from Pi's `light_service.py` to Pico's `firmware/main.py`.
+Pi becomes a thin HTTP-to-serial bridge.
+
+## New Serial Protocol
+
+| Input | Example | Response | Description |
+|-------|---------|----------|-------------|
+| `<int>` | `72` | *(none)* | Jaw amplitude 0-100, fire-and-forget |
+| `mood <mode>` | `mood thinking` | `OK` | Switch mood animation |
+| `jaw <mode>` | `jaw talking` | `OK` | Switch jaw animation |
+
+Mood modes: idle, listening, responding, pleasure, thinking, playful, commanding, love, sleep, off
+Jaw modes: idle, talking, off
+
+Bare integers are jaw amplitude (fast path, no response). This replaces per-LED serial flooding.
+
+## Pico Firmware Architecture
+
+Non-blocking main loop:
+1. Check serial (non-blocking poll)
+2. If data: integer -> jaw amplitude; string -> mode command
+3. Tick mood animation (based on mood_mode + time)
+4. Tick jaw animation (based on jaw_mode or amplitude)
+5. ~10-20ms frame pacing
+
+All 9 mood animations ported from light_service.py using `time.ticks_ms()`.
+Jaw: "level" mode maps 0-100 to 13 LEDs, "talking" mode oscillates autonomously.
+
+## Pi light_service.py Changes
+
+Remove: all animation logic, mood_buffer, per-LED helpers, main animation loop.
+Keep: HTTP API, serial connection management.
+POST /state -> sends `mood <state>\n`, waits for OK.
+POST /jaw/level -> sends `<level>\n`, fire-and-forget (no readline).
+
+## Files Changed
+
+- `firmware/main.py` - Full rewrite with animation engine
+- `light_service.py` - Strip down to HTTP-to-serial bridge