Add src/pattern/ module with 3 engine patterns:
- Breathe: smooth ramp up/down (~2.5s cycle, 1 engine)
- Heartbeat: double-pulse with long rest (~1.6s cycle, 1 engine)
- RGB cycle: phase-offset breathing via trigger sync (3 engines)
Patterns support both RGBW and 3-channel monochrome LED modes via
LED_MAP configuration. Main loop cycles through all 3 patterns (8s
each) while LP5562 runs them autonomously — MCU just idles.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
