fix(infra): implement resilient WebSocket heartbeat and unified connection state

[rajesh-puripanda]

Summary

Closes #465

Fixes the production WebSocket connection failure for 'Nyay Saarthi' (#465). This PR eliminates the UI state collisions and connection drops occurring between the Vercel frontend and Render backend.

Technical Changes

• Infrastructure (Heartbeat): Added a 30s heartbeat ping interval to prevent Render's 50s idle connection timeout.
• State Machine: Replaced ambiguous boolean flags with a centralized status enum (disconnected, connecting, connected, reconnecting, failed) to ensure UI consistency.
• Robustness:
  • Implemented an exponential backoff reconnection strategy (capped at 30s) that dynamically re-fetches auth tokens from localStorage to ensure valid handshake sessions.
  • Added defensive cleanup for onerror events and manual connection triggers to prevent orphaned timers/race conditions.
• UI/UX:
  • Centralized status management in NotificationBell.jsx via statusListeners.
  • Added a clear status indicator (dot/banner) to provide immediate feedback on connection health.
  • Suppressed "all caught up" empty states during failure to avoid confusing the user.

Testing Performed

• Verified heartbeat frames maintain persistent connection through idle periods.
• Tested state machine integrity (no conflicting banners).
• Validated token refresh during reconnection backoff.
• Confirmed cleanup of timers on component unmount and explicit disconnects.

Closes #465

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