M0: repo scaffold, backend skeleton, schema + migrations, dev compose, docs

- Apache-2.0, README, CONTRIBUTING, CODE_OF_CONDUCT, SECURITY, issue templates
- FastAPI app with /api/v1 healthz/readyz/system-status (honest AI disclosure)
- Full SQLAlchemy schema (users, devices, refresh tokens, recordings, assets,
  upload sessions, transcripts, summaries, tags, jobs, exports) + Alembic
  migrations incl. Postgres FTS tsvector columns
- Settings via SHONAR_* env only; local + S3 storage abstraction with
  path-traversal-safe keys
- Docker dev compose (postgres+redis, 127.0.0.1-only); CI workflow; scripts
- shared/openapi.json contract generated from app

.gitignore

@@ -0,0 +1,32 @@
+# --- Python ---
+__pycache__/
+*.py[cod]
+.venv/
+*.egg-info/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+dist/
+build/
+
+# --- Secrets & data ---
+.env
+.env.*
+!.env.example
+data/
+*.sqlite3
+
+# --- Android / Gradle ---
+android/.gradle/
+android/build/
+android/app/build/
+*.apk
+*.aab
+*.keystore
+local.properties
+
+# --- IDE / OS ---
+.idea/
+.vscode/
+*.swp
+.DS_Store