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>

api/tests/unit/test_config.py

@@ -59,3 +59,39 @@ def test_settings_jwt_expiry_override(monkeypatch):
 
     s = config_module.Settings()
     assert s.jwt_expiry_seconds == 3600
+
+
+def test_api_docs_enabled_default(monkeypatch):
+    _apply_env(monkeypatch)
+
+    import importlib
+
+    import app.config as config_module
+    importlib.reload(config_module)
+
+    s = config_module.Settings()
+    assert s.api_docs_enabled is True
+
+
+def test_api_docs_enabled_false(monkeypatch):
+    _apply_env(monkeypatch, {"API_DOCS_ENABLED": "false"})
+
+    import importlib
+
+    import app.config as config_module
+    importlib.reload(config_module)
+
+    s = config_module.Settings()
+    assert s.api_docs_enabled is False
+
+
+def test_api_docs_invalid_value_defaults_to_enabled(monkeypatch):
+    _apply_env(monkeypatch, {"API_DOCS_ENABLED": "not-a-bool"})
+
+    import importlib
+
+    import app.config as config_module
+    importlib.reload(config_module)
+
+    s = config_module.Settings()
+    assert s.api_docs_enabled is True