fix(dolt): proper server mode support for routing and storage

- FindDatabasePath now handles Dolt server mode (no local dir required)
- main.go uses NewFromConfigWithOptions for Dolt to read server settings
- Routing uses factory via callback to respect backend configuration
- Handle Dolt "database exists" error (error 1007) gracefully

Previously, Dolt server mode failed because:
1. FindDatabasePath required a local directory to exist
2. main.go bypassed server mode config when creating Dolt storage
3. Routing always opened SQLite regardless of backend config

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

internal/beads/beads.go

@@ -232,7 +232,11 @@ func findDatabaseInBeadsDir(beadsDir string, warnOnIssues bool) string {
 	if cfg, err := configfile.Load(beadsDir); err == nil && cfg != nil {
 		backend := cfg.GetBackend()
 		if backend == configfile.BackendDolt {
-			// For Dolt, check if the configured database directory exists
+			// For Dolt server mode, database is on the server - no local directory required
+			if cfg.IsDoltServerMode() {
+				return cfg.DatabasePath(beadsDir)
+			}
+			// For embedded Dolt, check if the configured database directory exists
 			doltPath := cfg.DatabasePath(beadsDir)
 			if info, err := os.Stat(doltPath); err == nil && info.IsDir() {
 				return doltPath