[AZ-263] Bootstrap: repo skeleton + Docker + CI + Alembic + Tier-1 tests

Implements the AZ-263 / E-BOOT initial structure task:

- Python src/-layout package `gps_denied_onboard/` with per-component
  interface stubs (14 components), type-only DTOs under `_types/`,
  shared helpers under `helpers/` (R14 LightGlue ownership), structured
  JSON logging, runtime composition root with env-var fail-fast gate,
  healthcheck module shared by Docker and CI smoke.
- CMake top-level + `cmake/{build_options,dependencies,strategies}.cmake`
  with the BUILD_* per-binary flags (ADR-002) and pinned external git
  refs for OKVIS2 / VINS-Mono / GTSAM / FAISS / OpenCV >=4.12.0.
- Three Dockerfiles (companion-tier1, operator-tooling,
  mock-suite-sat-service) + two compose files (dev + Tier-1 test).
- Four GitHub Actions workflows: ci.yml (lint/unit/integration/dual
  binary build/SBOM diff/security), ci-tier2.yml (self-hosted Jetson
  AC-bound NFTs), release.yml, cve-rescan.yml.
- Two CI gate scripts: `ci/sbom_diff.py` (deployment SBOM subset +
  R02 exclusion), `ci/opencv_pin_gate.py` (>=4.12.0 enforcement,
  D-CROSS-CVE-1).
- Alembic-driven Postgres 16 initial migration `0001_initial.py`
  mirroring satellite-provider tiles + flights + sector_classifications
  + manifests + engine_cache_entries (data_model.md s 2).
- Tier-1 test scaffolding: 95 passing unit tests covering every AC,
  per-component smoke tests, structured logging JSON output check,
  env-var gate check, healthcheck import check. Two CI-gated tests
  (cmake configure, actionlint) skip locally with explicit reasons.
- Batch report + code review report under `_docs/03_implementation/`.

Verdict: PASS_WITH_WARNINGS (two Low findings, both informational).
Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -0,0 +1,41 @@
+# gps-denied-onboard — environment variables
+# See _docs/02_document/module-layout.md and AZ-263_initial_structure.md § Environment Variables.
+
+# Required: selects the FC adapter at the composition root.
+# One of: ardupilot_plane | inav
+GPS_DENIED_FC_PROFILE=ardupilot_plane
+
+# Required: runtime tier gate; 1=workstation/CI, 2=Jetson production
+GPS_DENIED_TIER=1
+
+# Required: Postgres connection used by C6 (tile cache + descriptor index)
+DB_URL=postgresql://gps_denied:dev@db:5432/gps_denied
+
+# Required (dev/operator only): satellite-provider base URL for tile download
+# Not set in flight (no egress)
+SATELLITE_PROVIDER_URL=http://mock-sat:5100
+
+# Required: path to JSON camera calibration loaded at startup
+CAMERA_CALIBRATION_PATH=/fixtures/calibration/adti26.json
+
+# Required: structured log level (DEBUG | INFO | WARNING | ERROR)
+LOG_LEVEL=DEBUG
+
+# Required: structured log sink (console | journald | fdr)
+LOG_SINK=console
+
+# Required (production): per-flight MAVLink 2.0 signing key path
+# Dev key from tests/fixtures/mavlink_signing/dev_key in dev-tier1.
+MAVLINK_SIGNING_KEY=tests/fixtures/mavlink_signing/dev_key
+
+# CMake build flags (per-binary; honoured at compile time)
+BUILD_VINS_MONO=OFF
+BUILD_SALAD=OFF
+BUILD_C11_TILE_MANAGER=OFF
+
+# Required: C7 inference backend (tensorrt | pytorch_fp16 | onnx_trt_ep)
+INFERENCE_BACKEND=pytorch_fp16
+
+# Required: filesystem paths for runtime artifacts
+FDR_PATH=/var/lib/gps-denied/fdr
+TILE_CACHE_PATH=/var/lib/gps-denied/tiles