Expose DB connection error in /health response for debugging

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

app/main.py

@@ -10,10 +10,11 @@ logger = logging.getLogger("pops")
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
-    if check_db():
+    ok, msg = check_db()
+    if ok:
         logger.info("Database connection OK")
     else:
-        logger.warning("Database unreachable — check MYSQL_* environment variables")
+        logger.warning("Database unreachable: %s", msg)
     yield
 
 
@@ -27,8 +28,9 @@ def root():
 
 @app.get("/health")
 def health():
-    db_ok = check_db()
+    ok, msg = check_db()
     return {
-        "status": "ok" if db_ok else "degraded",
-        "db": "connected" if db_ok else "unreachable",
+        "status": "ok" if ok else "degraded",
+        "db": "connected" if ok else "unreachable",
+        "detail": msg,
     }