feat: run Hevy bridge locally on Pixel, no Tailscale in gym

- Add HevyBridge Android APK with AccessibilityService + localhost HTTP API
- Fitbit companion now polls http://127.0.0.1:18090 instead of cloud backend
- Watch actions route to local bridge for set_done / skip_rest / timer_adjust
- Restore backend schema/action endpoint and make cloud backend debug/download only
- CI now builds both app.fba and hevy-bridge.apk release artifacts
- Update docs/handoff for phone-local production architecture