Implement stricter daemon lock file validation (bd-161)

- Add JSON format to daemon.lock with database path, version, PID, and timestamp
- Validate database path on client connection (fail if mismatch)
- Backward compatible with old plain-PID lock files
- Add comprehensive tests for JSON format and validation
- Update all lock acquisition callsites to pass database path

Amp-Thread-ID: https://ampcode.com/threads/T-137e6a9c-b690-4ade-9bec-13fcd7d0e4ed
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/daemon_test.go

@@ -132,7 +132,8 @@ func TestIsDaemonRunning_CurrentProcess(t *testing.T) {
 
 	// Acquire the daemon lock to simulate a running daemon
 	beadsDir := filepath.Dir(pidFile)
-	lock, err := acquireDaemonLock(beadsDir, false)
+	dbPath := filepath.Join(beadsDir, "beads.db")
+	lock, err := acquireDaemonLock(beadsDir, dbPath)
 	if err != nil {
 		t.Fatalf("Failed to acquire daemon lock: %v", err)
 	}