feat: add database health check endpoint

backend/app.py

@@ -21,7 +21,7 @@
 from routes.plugins import router as plugins_router
 from routes.export import router as export_router
 from routes.settings import router as settings_router
-from services.db_service import init_db
+from services.db_service import init_db, get_db
 
 logging.basicConfig(
     level=logging.INFO,
@@ -90,3 +90,12 @@ async def root():
 @app.get("/health", tags=["Health"])
 async def health():
     return {"status": "healthy"}
+
+@app.get("/health/db", tags=["Health"])
+async def db_health():
+    try:
+        with get_db() as conn:
+            conn.execute("SELECT 1")
+        return {"status": "healthy"}
+    except Exception:
+        return {"status": "unhealthy"}

backend/tests/test_api.py

@@ -29,6 +29,11 @@ def test_health():
     assert r.json()["status"] == "healthy"
 
 
+def test_db_health():
+    r = client.get("/health/db")
+    assert r.status_code == 200
+    assert r.json()["status"] == "healthy"
+
 # ─── Sessions ────────────────────────────────────────────
 def test_create_session():
     r = client.post("/api/sessions/", json={"title": "Test Chat", "model": "llama3"})