feat: add proper HTTP status codes to all API error responses

- 217 error returns across 18 route files + api.py now use JSONResponse
  with appropriate HTTP status codes instead of returning HTTP 200
- Status code distribution: 500 (121), 400 (39), 503 (28), 404 (24), 409 (3), 502 (2)
- Fixed language.py tuple-return bug (was serializing as JSON array)
- Fixed bare except clauses in bipolar_mode.py and voice.py
- Body-level error schemas preserved (status/error + success/error patterns)
  so web UI continues working without changes
- chat.py (SSE) unchanged: errors sent within stream protocol
- All 170 tests pass

bot/routes/core.py

@@ -1,7 +1,7 @@
 """Core routes: index, logs, prompts, status, conversation."""
 
 from fastapi import APIRouter
-from fastapi.responses import FileResponse
+from fastapi.responses import FileResponse, JSONResponse
 import globals
 from server_manager import server_manager
 from utils.conversation_history import conversation_history
@@ -26,7 +26,7 @@ def get_logs():
         last_100 = lines[-100:] if len(lines) >= 100 else lines
         return "".join(last_100)
     except Exception as e:
-        return f"Error reading log file: {e}"
+        return JSONResponse(status_code=500, content={"status": "error", "message": f"Error reading log file: {e}"})
 
 
 @router.get("/prompt")