fix: post-audit — runtime bugs, functional gaps, docs, hardening

Phase A — Runtime bugs:
  - SSE: add push_event() method to SSEEventStreamer (was missing, masked by mocks)
  - MAVLink: satellites_visible=10 (was 0, triggers ArduPilot failsafe)
  - MAVLink: horiz_accuracy=sqrt(P[0,0]+P[1,1]) per spec (was sqrt(avg))
  - MAVLink: MEDIUM confidence → fix_type=3 per solution.md (was 2)

Phase B — Functional gaps:
  - handle_user_fix() injects operator GPS into ESKF with noise=500m
  - app.py uses create_vo_backend() factory (was hardcoded SequentialVO)
  - ESKF: Mahalanobis gating on satellite updates (rejects outliers >5σ)
  - ESKF: public accessors (position, quaternion, covariance, last_timestamp)
  - Processor: no more private ESKF field access

Phase C — Documentation:
  - README: correct API endpoints, CLI command, 40+ env vars documented
  - Dockerfile: ENV prefixes match pydantic-settings (DB_, SATELLITE_, MAVLINK_)
  - tech_stack.md marked ARCHIVED (contradicts solution.md)

Phase D — Hardening:
  - JWT auth middleware (AUTH_ENABLED=false default, verify_token on /flights)
  - TLS config env vars (AUTH_SSL_CERTFILE, AUTH_SSL_KEYFILE)
  - SHA-256 tile manifest verification in SatelliteDataManager
  - AuthConfig, ESKFSettings, MAVLinkConfig, SatelliteConfig in config.py

Also: conftest.py shared fixtures, download_tiles.py, convert_to_trt.py scripts,
config wiring into app.py lifespan, config-driven ESKF, calculate_precise_angle fix.

Tests: 196 passed / 8 skipped. Ruff clean.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/gps_denied/schemas/eskf.py

@@ -51,6 +51,9 @@ class ESKFConfig(BaseModel):
     init_accel_bias_var: float = 0.01      # (m/s^2)^2
     init_gyro_bias_var: float = 1e-6       # (rad/s)^2
 
+    # Mahalanobis outlier rejection (chi-squared threshold for 3-DOF at 5-sigma)
+    mahalanobis_threshold: float = 16.27   # chi2(3, 0.99999) ≈ 5-sigma gate
+
 
 class ESKFState(BaseModel):
     """Full ESKF nominal state snapshot."""

src/gps_denied/schemas/mavlink.py

@@ -28,7 +28,7 @@ class GPSInputMessage(BaseModel):
     speed_accuracy: float    # m/s
     horiz_accuracy: float    # m
     vert_accuracy: float     # m
-    satellites_visible: int = 0
+    satellites_visible: int = 10  # synthetic — prevents ArduPilot satellite-count failsafes
 
 
 class IMUMessage(BaseModel):