Phase B4: fuse mobile GPS/IMU into camera calibration

[mandarwagh9]

What & why

Phase B4. The mobile client streams GPS (watchPosition) + IMU (DeviceOrientationEvent), but the backend was receiving and discarding the sensor_data message (pass). Now it's fused into the camera calibration.

⚠️ Stacked on the chain (#11 → … → #4). Auto-retargets as the stack merges.

Changes

• New app/infrastructure/geo.py — gps_to_local(): equirectangular projection of lat/lng to local east/north metres.
• World model update_camera_sensor() — GPS → local position (relative to GPS_REFERENCE_*, or the first fix becomes the origin) and DeviceOrientation alpha/beta/gamma → camera rotation (roll/pitch/yaw). Overrides the auto-default calibration for that camera; missing fields fall back to any existing calibration. Added to the WorldModelRepository port as a concrete no-op default.
• main.py — the /ws/camera handler now forwards sensor_data to the world model instead of discarding it (verified the fused keys match what cameraStreamAdapter.js actually sends).
• README — flipped GPS/IMU fusion from 🔭 planned to ✅ implemented (status table, platform row, mobile handshake).

Tests (TDD)

8 new:

• test_geo.py — reference→origin, north offset → +y (~111 m), east offset → +x scaled by cos(lat)
• test_gps_fusion.py — first fix becomes origin, second fix north → +y, configured reference used, orientation → rotation (yaw), no-data → no-op

Verification

• ruff clean · mypy clean (18 files) · 103 tests pass (was 95).
• Coverage 58% → 59% (floor 50%).

🤖 Generated with Claude Code

[mandarwagh9]

Superseded — all commits from this phase landed on main via the merge of #13 (the top of the stack, which contains every phase commit). Closing to tidy up; the work is fully merged.