fix: resolve CI lint errors in Sidebar, TypingIndicator, and useGateway

- Sidebar: replace useEffect setState with callback pattern for filter reset
- TypingIndicator: initialize useRef with 0 instead of impure Date.now()
- TypingIndicator: remove redundant setElapsed(0) from mount effect
- useGateway: remove unused eslint-disable directive

src/hooks/useGateway.ts

@@ -314,7 +314,6 @@ export function useGateway() {
     const stored = getStoredCredentials();
     if (stored) {
       // Init on mount — setupClient sets state as part of establishing the connection
-      // eslint-disable-next-line react-hooks/set-state-in-effect
       setupClient(stored.url, stored.token);
     } else {
       setAuthenticated(false);