Add daemon health check endpoint (bd-146)

- Add OpHealth RPC operation to protocol
- Implement handleHealth() with DB ping and 1s timeout
- Returns status (healthy/degraded/unhealthy), uptime, cache metrics
- Update TryConnect() to use health check instead of ping
- Add 'bd daemon --health' CLI command with JSON output
- Track cache hits/misses for metrics
- Unhealthy daemon triggers automatic fallback to direct mode
- Health check completes in <2 seconds

Amp-Thread-ID: https://ampcode.com/threads/T-1a4889f3-77cf-433a-a704-e1c383929f48
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/daemon.go

@@ -38,10 +38,12 @@ The daemon will:
 - Auto-import when remote changes detected
 
 Use --stop to stop a running daemon.
-Use --status to check if daemon is running.`,
+Use --status to check if daemon is running.
+Use --health to check daemon health and metrics.`,
 	Run: func(cmd *cobra.Command, args []string) {
 		stop, _ := cmd.Flags().GetBool("stop")
 		status, _ := cmd.Flags().GetBool("status")
+		health, _ := cmd.Flags().GetBool("health")
 		interval, _ := cmd.Flags().GetDuration("interval")
 		autoCommit, _ := cmd.Flags().GetBool("auto-commit")
 		autoPush, _ := cmd.Flags().GetBool("auto-push")
@@ -64,6 +66,11 @@ Use --status to check if daemon is running.`,
 			return
 		}
 
+		if health {
+			showDaemonHealth(global)
+			return
+		}
+
 		if stop {
 			stopDaemon(pidFile)
 			return
@@ -119,6 +126,7 @@ func init() {
 	daemonCmd.Flags().Bool("auto-push", false, "Automatically push commits")
 	daemonCmd.Flags().Bool("stop", false, "Stop running daemon")
 	daemonCmd.Flags().Bool("status", false, "Show daemon status")
+	daemonCmd.Flags().Bool("health", false, "Check daemon health and metrics")
 	daemonCmd.Flags().String("log", "", "Log file path (default: .beads/daemon.log)")
 	daemonCmd.Flags().Bool("global", false, "Run as global daemon (socket at ~/.beads/bd.sock)")
 	rootCmd.AddCommand(daemonCmd)
@@ -250,6 +258,78 @@ func showDaemonStatus(pidFile string, global bool) {
 	}
 }
 
+func showDaemonHealth(global bool) {
+	var socketPath string
+	if global {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: cannot get home directory: %v\n", err)
+			os.Exit(1)
+		}
+		socketPath = filepath.Join(home, ".beads", "bd.sock")
+	} else {
+		beadsDir, err := ensureBeadsDir()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		socketPath = filepath.Join(beadsDir, "bd.sock")
+	}
+	
+	client, err := rpc.TryConnect(socketPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error connecting to daemon: %v\n", err)
+		os.Exit(1)
+	}
+	
+	if client == nil {
+		fmt.Println("✗ Daemon is not running")
+		os.Exit(1)
+	}
+	defer client.Close()
+	
+	health, err := client.Health()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error checking health: %v\n", err)
+		os.Exit(1)
+	}
+	
+	if jsonOutput {
+		data, _ := json.MarshalIndent(health, "", "  ")
+		fmt.Println(string(data))
+		return
+	}
+	
+	statusIcon := "✓"
+	if health.Status == "unhealthy" {
+		statusIcon = "✗"
+	} else if health.Status == "degraded" {
+		statusIcon = "⚠"
+	}
+	
+	fmt.Printf("%s Daemon Health: %s\n", statusIcon, health.Status)
+	fmt.Printf("  Version: %s\n", health.Version)
+	fmt.Printf("  Uptime: %.1f seconds\n", health.Uptime)
+	fmt.Printf("  Cache Size: %d databases\n", health.CacheSize)
+	fmt.Printf("  Cache Hits: %d\n", health.CacheHits)
+	fmt.Printf("  Cache Misses: %d\n", health.CacheMisses)
+	
+	if health.CacheHits+health.CacheMisses > 0 {
+		hitRate := float64(health.CacheHits) / float64(health.CacheHits+health.CacheMisses) * 100
+		fmt.Printf("  Cache Hit Rate: %.1f%%\n", hitRate)
+	}
+	
+	fmt.Printf("  DB Response Time: %.2f ms\n", health.DBResponseTime)
+	
+	if health.Error != "" {
+		fmt.Printf("  Error: %s\n", health.Error)
+	}
+	
+	if health.Status == "unhealthy" {
+		os.Exit(1)
+	}
+}
+
 func stopDaemon(pidFile string) {
 	if isRunning, pid := isDaemonRunning(pidFile); !isRunning {
 		fmt.Println("Daemon is not running")