feat(cli): restructure CLI commands for better UX

- Add top-level `multica login` that combines auth + workspace auto-discovery
- Restructure daemon into subcommands: start, stop, status, logs
- Add background daemon mode with PID management
- Add daemon deregistration on shutdown (new API endpoint + SQL query)
- Remove unused commands: runtime list, status, agent get/delete/stop
- Make `config` show config directly instead of requiring `config show`
- Update README to reflect new CLI structure

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/cmd/server/router.go

@@ -86,6 +86,7 @@ func NewRouter(pool *pgxpool.Pool, hub *realtime.Hub, bus *events.Bus) chi.Route
 		r.Post("/pairing-sessions/{token}/claim", h.ClaimDaemonPairingSession)
 
 		r.Post("/register", h.DaemonRegister)
+		r.Post("/deregister", h.DaemonDeregister)
 		r.Post("/heartbeat", h.DaemonHeartbeat)
 
 		r.Post("/runtimes/{runtimeId}/tasks/claim", h.ClaimTaskByRuntime)