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>

tests/conftest.py

@@ -0,0 +1,61 @@
+"""Shared test fixtures for GPS-denied-onboard test suite."""
+
+from unittest.mock import AsyncMock, MagicMock
+
+import numpy as np
+import pytest
+
+from gps_denied.core.coordinates import CoordinateTransformer
+from gps_denied.core.models import ModelManager
+from gps_denied.schemas import CameraParameters, GPSPoint
+
+# ---------------------------------------------------------------
+# Common constants
+# ---------------------------------------------------------------
+
+TEST_ORIGIN = GPSPoint(lat=49.0, lon=32.0)
+TEST_CAMERA = CameraParameters(
+    focal_length=4.5,
+    sensor_width=6.17,
+    sensor_height=4.55,
+    resolution_width=640,
+    resolution_height=480,
+)
+
+
+# ---------------------------------------------------------------
+# Shared fixtures
+# ---------------------------------------------------------------
+
+@pytest.fixture
+def mock_repo():
+    """Mock FlightRepository."""
+    return MagicMock()
+
+
+@pytest.fixture
+def mock_streamer():
+    """Mock SSEEventStreamer with async push_event."""
+    s = MagicMock()
+    s.push_event = AsyncMock()
+    return s
+
+
+@pytest.fixture
+def model_manager():
+    """Singleton ModelManager (mock engines)."""
+    return ModelManager()
+
+
+@pytest.fixture
+def coord_transformer():
+    """CoordinateTransformer with a preset test ENU origin."""
+    ct = CoordinateTransformer()
+    ct.set_enu_origin("test_flight", TEST_ORIGIN)
+    return ct
+
+
+@pytest.fixture
+def sample_image():
+    """Random 200x200 RGB image for pipeline tests."""
+    return np.random.randint(0, 255, (200, 200, 3), dtype=np.uint8)