fix(dolt): server mode should support multi-process access

Code review fix: In server mode, Dolt connects to an external sql-server
and should NOT be single-process-only. The whole point of server mode is
to enable multi-writer access.

Changes:
- Add Config.GetCapabilities() method that considers server mode
- Update daemon_guard, daemon_autostart, daemons, main to use GetCapabilities()
- Add TestGetCapabilities test
- Update init command help text to document server mode flags

The existing CapabilitiesForBackend(string) is kept for backward compatibility
but now includes a note to use Config.GetCapabilities() when the full config
is available.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/daemon_autostart.go

@@ -69,7 +69,8 @@ func singleProcessOnlyBackend() bool {
 	if err != nil || cfg == nil {
 		return false
 	}
-	return configfile.CapabilitiesForBackend(cfg.GetBackend()).SingleProcessOnly
+	// Use GetCapabilities() to properly handle Dolt server mode
+	return cfg.GetCapabilities().SingleProcessOnly
 }
 
 // shouldAutoStartDaemon checks if daemon auto-start is enabled