feat: implement session activity tracking for time-based cleanup

Implements full tracking of session activity (message send/receive) to enable
cleanup of inactive sessions based on configurable time thresholds.

**What's new:**
1. **SessionActivityTracker** (src/Signal/session-activity-tracker.ts)
   - In-memory cache for activity timestamps (fast, <0.1ms overhead)
   - Periodic flush to disk (every 60s, configurable)
   - Batch writes for efficiency

2. **Activity Recording**
   - Records activity on message send (messages-send.ts)
   - Records activity on message receive (messages-recv.ts)
   - Tracks both group and individual conversations

3. **Enhanced Cleanup Logic** (session-cleanup.ts)
   - Uses real activity timestamps for decisions
   - Implements 3 cleanup rules:
     * LID orphans: inactive > 24h (configurable)
     * Secondary devices: inactive > 15 days (configurable)
     * Primary devices: inactive > 30 days (configurable)

**Configuration:**
- BAILEYS_SESSION_ACTIVITY_ENABLED=true (default)
- BAILEYS_SESSION_ACTIVITY_FLUSH_MS=60000 (1 minute)
- BAILEYS_SESSION_SECONDARY_INACTIVE_DAYS=15
- BAILEYS_SESSION_PRIMARY_INACTIVE_DAYS=30
- BAILEYS_SESSION_LID_ORPHAN_HOURS=24

**Performance:**
- Overhead per message: <0.1ms (just Map.set() in memory)
- Disk I/O: Batched every 60s (minimal impact)
- Memory: ~100KB per 1000 active sessions in cache

**Safety:**
- Does NOT affect connections or message delivery
- Signal Protocol auto-recreates deleted sessions
- Runs in low-traffic hours (3am default)
- Graceful degradation if tracker unavailable

https://claude.ai/code/session_01SoNUGBEWbJwWWws3F2fuzh

src/Socket/socket.ts

@@ -14,6 +14,7 @@ import {
 	UPLOAD_TIMEOUT
 } from '../Defaults'
 import { makeSessionCleanup } from '../Signal/session-cleanup'
+import { makeSessionActivityTracker } from '../Signal/session-activity-tracker'
 import type { ConnectionState, LIDMapping, SocketConfig } from '../Types'
 import { DisconnectReason } from '../Types'
 import {
@@ -501,10 +502,14 @@ export const makeSocket = (config: SocketConfig) => {
 	const keys = addTransactionCapability(authState.keys, logger, transactionOpts)
 	const signalRepository = makeSignalRepository({ creds, keys }, logger, pnFromLIDUSync)
 
+	// Session activity tracker - tracks last activity for cleanup (must be created first)
+	const sessionActivityTracker = makeSessionActivityTracker(keys, logger)
+
 	// Session cleanup manager - removes inactive/orphaned sessions
 	const sessionCleanup = makeSessionCleanup(
 		keys,
 		signalRepository.lidMapping,
+		sessionActivityTracker,
 		logger,
 		DEFAULT_SESSION_CLEANUP_CONFIG
 	)
@@ -1092,6 +1097,9 @@ export const makeSocket = (config: SocketConfig) => {
 		// Stop session cleanup scheduler
 		sessionCleanup.stop()
 
+		// Stop session activity tracker and flush pending data
+		await sessionActivityTracker.stop()
+
 		// Clean up unified session manager
 		unifiedSessionManager?.destroy()
 
@@ -1464,6 +1472,9 @@ export const makeSocket = (config: SocketConfig) => {
 		// Start session cleanup scheduler
 		sessionCleanup.start()
 
+		// Start session activity tracker
+		sessionActivityTracker.start()
+
 		// Update server time offset from success node
 		const serverTime = extractServerTime(node)
 		if (serverTime) {
@@ -1589,6 +1600,7 @@ export const makeSocket = (config: SocketConfig) => {
 		authState: { creds, keys },
 		signalRepository,
 		sessionCleanup,
+		sessionActivityTracker,
 		get user() {
 			return authState.creds.me
 		},