fix(serverless): disable Clear saved API key while the worker is enabled

The checkbox read "Clear saved API key (disable pool first)", but the
panel never defines "pool" and saving with it ticked on an enabled worker
was rejected by the backend.

- Disable the checkbox while the worker is enabled, with a tooltip saying
  to turn the worker off first. Also disable it when no key is saved.
- Use "worker" instead of "pool" in user-facing serverless errors, the
  serverless guide and the README entry.

api/orchestration/serverless_runtime.py

@@ -130,7 +130,7 @@ class ServerlessManager:
             self.pool_limits[pool_id] = current
         elif current[0] != limit:
             if self.pool_is_active(pool_id):
-                raise ValueError("Wait for this serverless pool's current jobs before changing concurrency")
+                raise ValueError("Wait for this serverless worker's current jobs before changing concurrency")
             current = (limit, asyncio.Semaphore(limit))
             self.pool_limits[pool_id] = current
         return current[1]
@@ -320,7 +320,7 @@ class ServerlessManager:
         async with self.recovery_lock:
             record = next((r for r in self._detached_records(worker_id) if r["record_id"] == record_id), None)
             if record is None:
-                raise ValueError("Unresolved inactive job not found for this pool")
+                raise ValueError("Unresolved inactive job not found for this worker")
             self.ledger.update(record_id, status="RESOLVED", updated_at=time.time(),
                                error="Recovery explicitly acknowledged after operator checked Runpod; not provider-confirmed")
         await self._notify_capacity()