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>

internal/configfile/configfile.go

@@ -176,17 +176,35 @@ type BackendCapabilities struct {
 
 // CapabilitiesForBackend returns capabilities for a backend string.
 // Unknown backends are treated conservatively as single-process-only.
+//
+// Note: For Dolt, this returns SingleProcessOnly=true for embedded mode.
+// Use Config.GetCapabilities() when you have the full config to properly
+// handle server mode (which supports multi-process access).
 func CapabilitiesForBackend(backend string) BackendCapabilities {
 	switch strings.TrimSpace(strings.ToLower(backend)) {
 	case "", BackendSQLite:
 		return BackendCapabilities{SingleProcessOnly: false}
 	case BackendDolt:
+		// Embedded Dolt is single-process-only.
+		// Server mode is handled by Config.GetCapabilities().
 		return BackendCapabilities{SingleProcessOnly: true}
 	default:
 		return BackendCapabilities{SingleProcessOnly: true}
 	}
 }
 
+// GetCapabilities returns the backend capabilities for this config.
+// Unlike CapabilitiesForBackend(string), this considers Dolt server mode
+// which supports multi-process access.
+func (c *Config) GetCapabilities() BackendCapabilities {
+	backend := c.GetBackend()
+	if backend == BackendDolt && c.IsDoltServerMode() {
+		// Server mode supports multi-writer, so NOT single-process-only
+		return BackendCapabilities{SingleProcessOnly: false}
+	}
+	return CapabilitiesForBackend(backend)
+}
+
 // GetBackend returns the configured backend type, defaulting to SQLite.
 func (c *Config) GetBackend() string {
 	if c.Backend == "" {