feat(config): allow runtime_fallback to be configured as boolean

Enable simple boolean configuration for runtime_fallback:
- "runtime_fallback": true - Enable with defaults
- "runtime_fallback": false - Disable
- "runtime_fallback": { ... } - Advanced object config (existing)

Updated schema, event handler, chat-message handler, and session hooks
to handle both boolean and object formats.

src/config/schema/oh-my-opencode-config.ts

@@ -44,7 +44,12 @@ export const OhMyOpenCodeConfigSchema = z.object({
   auto_update: z.boolean().optional(),
   skills: SkillsConfigSchema.optional(),
   ralph_loop: RalphLoopConfigSchema.optional(),
-  runtime_fallback: RuntimeFallbackConfigSchema.optional(),
+  /**
+   * Enable runtime fallback (default: true)
+   * Set to false to disable, or use object for advanced config:
+   * { "enabled": true, "retry_on_errors": [400, 429], "timeout_seconds": 30 }
+   */
+  runtime_fallback: z.union([z.boolean(), RuntimeFallbackConfigSchema]).optional(),
   background_task: BackgroundTaskConfigSchema.optional(),
   notification: NotificationConfigSchema.optional(),
   babysitting: BabysittingConfigSchema.optional(),