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/sync.go

@@ -361,6 +361,9 @@ Use --merge to merge the sync branch back to main branch.`,
 				}
 			}
 
+			// Clear sync state on successful sync (daemon backoff/hints)
+			_ = ClearSyncState(beadsDir)
+
 			fmt.Println("\n✓ Sync complete")
 			return
 		}
@@ -711,6 +714,11 @@ Use --merge to merge the sync branch back to main branch.`,
 				skipFinalFlush = true
 			}
 
+			// Clear sync state on successful sync (daemon backoff/hints)
+			if bd := beads.FindBeadsDir(); bd != "" {
+				_ = ClearSyncState(bd)
+			}
+
 			fmt.Println("\n✓ Sync complete")
 		}
 	},