Add RPC diagnostics with BD_RPC_DEBUG env var

- Add BD_RPC_DEBUG=1 for lightweight timing logs to stderr
- Log socket path, socket exists check, dial timing, health check timing
- Improve daemon status message when lock not held
- Helps field triage of connection issues without verbose daemon logs
- Fixes bd-j7e2

.beads/bd.sock.startlock

@@ -0,0 +1 @@
+36165