[AZ-390] [AZ-392] C8 FC/GCS adapter foundation + covariance projector

Adds the C8 foundation:
- FcAdapter / GcsAdapter / ReplaySink Protocols + contract DTOs in
  _types/fc.py (PortConfig, FcKind, FlightState, GpsStatus, Severity,
  TelemetryKind, FcTelemetryFrame, FlightStateSignal, GpsHealth,
  OperatorCommand, Subscription, Imu/Attitude samples).
- Disjoint FcAdapterError / GcsAdapterError trees with
  SourceSetSwitchNotSupportedError <: SourceSetSwitchError per AC-9.
- FcConfig + GcsConfig cross-cutting Config blocks with config-load
  validation (unknown strategy rejected at __post_init__).
- runtime_root/fc_factory.py: build_fc_adapter / build_gcs_adapter
  with BUILD_FC_*/BUILD_GCS_* flag gating + INFO log on load +
  single-writer outbound-thread binding.
- CovarianceProjector (helper, AZ-392): 6x6 -> 3x3 -> 2x2 ->
  sqrt(lambda_max) reduction; AP returns float m, iNav returns int mm
  with uint16 clamp + WARN + FDR record. Non-SPD / NaN / wrong-shape
  raise FcEmitError and emit an FDR ERROR record carrying frame_id.

Contracts:
- composition_root_protocol.md 1.1.0 -> 1.2.0 (added fc/gcs blocks +
  build_fc_adapter / build_gcs_adapter + outbound-thread binding).
- fc_adapter_protocol.md unchanged (this batch implements v1.0.0).

Tests: 410 pass / 2 skip / 0 fail (+53 new tests in batch 8).

AZ-391 (inbound subscription) deferred to batch 9 — pulls YAMSPy as
a new external dependency (iNav MSP2 decode).

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/test_ac1_scaffold_layout.py

@@ -44,7 +44,7 @@ REQUIRED_PATHS: tuple[str, ...] = (
     "ci/sbom_diff.py",
     "ci/opencv_pin_gate.py",
     "src/gps_denied_onboard/__init__.py",
-    "src/gps_denied_onboard/runtime_root.py",
+    "src/gps_denied_onboard/runtime_root/__init__.py",
     "src/gps_denied_onboard/healthcheck.py",
     "src/gps_denied_onboard/_types/__init__.py",
     "src/gps_denied_onboard/helpers/__init__.py",