feat(daemon): add sync backoff and consolidate hints into tips

Daemon sync improvements:
- Adds exponential backoff on sync failures (30s → 1m → 2m → 5m → 10m → 30m cap)
- Tracks sync state in .beads/sync-state.json (NeedsManualSync, FailureCount, BackoffUntil)
- Resets backoff on daemon start and manual bd sync
- Adds sync-state.json to default .gitignore

Tips consolidation (following ox-cli pattern):
- Moves sync conflict hint from hints.go into tips.go
- Proactive health checks trump educational tips
- Uses InjectTip() with high priority (200) and 100% probability for urgent warnings
- Removes deprecated hints.go

cmd/bd/daemon.go

@@ -355,6 +355,11 @@ func runDaemonLoop(interval time.Duration, autoCommit, autoPush, autoPull, local
 
 	// Check for multiple .db files (ambiguity error)
 	beadsDir := filepath.Dir(daemonDBPath)
+
+	// Reset backoff on daemon start (fresh start, but preserve NeedsManualSync hint)
+	if !localMode {
+		ResetBackoffOnDaemonStart(beadsDir)
+	}
 	matches, err := filepath.Glob(filepath.Join(beadsDir, "*.db"))
 	if err == nil && len(matches) > 1 {
 		// Filter out backup files (*.backup-*.db, *.backup.db)