feat: disable Ralph/Todo tracker auto-enable by default

Ralph tracker no longer auto-enables on pattern detection. It must be
explicitly enabled per-session (via API) or globally via the new
`ralphEnabled` AppConfig setting. Adds GET/PUT /api/config endpoints
for runtime configuration. Spawn agent ralph enable is unchanged.

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

src/types.ts

@@ -229,6 +229,8 @@ export interface AppConfig {
   respawn: RespawnConfig;
   /** Last used case name (for default selection) */
   lastUsedCase: string | null;
+  /** Whether Ralph/Todo tracker is globally enabled for all new sessions */
+  ralphEnabled: boolean;
 }
 
 // ========== Output Types ==========
@@ -564,6 +566,7 @@ export const DEFAULT_CONFIG: AppConfig = {
     sendInit: true,                // send /init after /clear
   },
   lastUsedCase: null,
+  ralphEnabled: false,
 };
 
 // ========== Inner Loop Tracking Types ==========