Feat: Gate API docs endpoints behind API_DOCS_ENABLED env var

When API_DOCS_ENABLED=false, FastAPI registers no routes for /docs,
/redoc, or /openapi.json, returning 404 for all three. Default is true
for backwards compatibility. Invalid values fall back to true (FR-007).

Fix: Remove tests/ and alembic/ from api/.dockerignore so the test
Dockerfile (which uses COPY . .) includes the test suite; Dockerfile.prod
is unaffected as it only copies app/ explicitly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

specs/012-api-docs-gate/quickstart.md

@@ -0,0 +1,42 @@
+# Quickstart: API Documentation Visibility Gate
+
+## Verify docs are disabled
+
+```bash
+# Start API with docs disabled
+API_DOCS_ENABLED=false uvicorn app.main:app --reload
+
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/docs        # → 404
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/redoc       # → 404
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/openapi.json # → 404
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/api/v1/health # → 200
+```
+
+## Verify docs are enabled (default)
+
+```bash
+# Start API without the flag (or with it set to true)
+uvicorn app.main:app --reload
+
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/docs         # → 200
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/redoc        # → 200
+curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/openapi.json # → 200
+```
+
+## Integration test scenarios
+
+### Scenario 1: flag disabled — all three docs endpoints return 404
+
+Start a test client with `API_DOCS_ENABLED=false` injected into settings. Assert each of the three endpoint paths returns 404. Assert `/api/v1/health` returns 200.
+
+### Scenario 2: flag enabled (default) — docs endpoints return 200
+
+Start a test client without the flag (or with `API_DOCS_ENABLED=true`). Assert each of the three endpoint paths returns 200.
+
+### Scenario 3: invalid flag value — app starts, docs enabled
+
+Set `API_DOCS_ENABLED=not-a-bool`. The app must start without error. Docs must be accessible (safe fallback to enabled).
+
+### Scenario 4: flag absent — docs enabled (backwards compatibility)
+
+Start the app with no `API_DOCS_ENABLED` variable set. Assert docs endpoints return 200 — identical to pre-feature behaviour.