feat(daemon): add GET /status endpoint (bd-148)

- Add OpStatus operation and StatusResponse type to RPC protocol
- Add workspacePath and dbPath fields to Server struct
- Implement handleStatus() handler with daemon metadata
- Track last activity time with atomic.Value
- Add client.Status() method
- Check for exclusive locks via ShouldSkipDatabase()
- Update all test files to use new NewServer signature
- Add comprehensive status endpoint test

Closes bd-148

internal/rpc/protocol.go

@@ -7,6 +7,7 @@ import (
 // Operation constants for all bd commands
 const (
 	OpPing            = "ping"
+	OpStatus          = "status"
 	OpHealth          = "health"
 	OpMetrics         = "metrics"
 	OpCreate          = "create"
@@ -165,6 +166,19 @@ type PingResponse struct {
 	Version string `json:"version"`
 }
 
+// StatusResponse represents the daemon status metadata
+type StatusResponse struct {
+	Version              string  `json:"version"`                  // Server/daemon version
+	WorkspacePath        string  `json:"workspace_path"`           // Absolute path to workspace root
+	DatabasePath         string  `json:"database_path"`            // Absolute path to database file
+	SocketPath           string  `json:"socket_path"`              // Path to Unix socket
+	PID                  int     `json:"pid"`                      // Process ID
+	UptimeSeconds        float64 `json:"uptime_seconds"`           // Time since daemon started
+	LastActivityTime     string  `json:"last_activity_time"`       // ISO 8601 timestamp of last request
+	ExclusiveLockActive  bool    `json:"exclusive_lock_active"`    // Whether an exclusive lock is held
+	ExclusiveLockHolder  string  `json:"exclusive_lock_holder,omitempty"` // Lock holder name if active
+}
+
 // HealthResponse is the response for a health check operation
 type HealthResponse struct {
 	Status         string  `json:"status"`                   // "healthy", "degraded", "unhealthy"