#219 Typing indicators (ephemeral, never stored) FIXED

[felladaniel36-hash]

Description

Implemented real-time typing_start and typing_stop Socket.IO event handling relayed via Pub/Sub conversation rooms with strictly zero database writes:

• Backend Pub/Sub Relaying & Sanitization: Replaced blind broadcast handlers in messaging.ts with explicit payload construction { conversationId, userId, ...(deviceId ? { deviceId } : {}) }, permanently guaranteeing that draft message content is never relayed. Fast-path verifies room membership via socket.rooms.has(conversationId) to avoid unnecessary database queries.
• Auto-Expiration & Event Cleanup: Added per-socket typingTimers tracking active typing sessions with a 5-second inactivity timeout. Automatically dispatches typing_stop upon timer expiration, and instantly clears typing indicators when a socket disconnects or emits send_message.
• Frontend Emitters Integration: Instrumented MessageInput.tsx with debounced timers (2000ms delay) to emit real-time typing events as users type and immediately stop typing indicators upon sending text or confirming Soroban token transfers.
• Build & Type Fixes: Resolved TypeScript build issues in conversations.ts and treasury.ts.
• Unit Testing: Created comprehensive test suite apps/backend/src/__tests__/typing.test.ts validating all acceptance criteria (zero DB writes, timeout auto-clearing, room-member isolation, content stripping, and disconnect cleanup).

Type of change

• Bug fix

• New feature

• Documentation update

• Other

Checklist

• I have read the contributing guidelines

• I have tested my changes locally

• My code follows the project's coding standards

CLOSE #219

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[felladaniel36-hash]

PLEASE REVIEW... AND PING ME BACK