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/plugin/hooks/create-session-hooks.ts

@@ -245,10 +245,15 @@ export function createSessionHooks(args: {
     ? safeHook("anthropic-effort", () => createAnthropicEffortHook())
     : null
 
+  const runtimeFallbackConfig =
+    typeof pluginConfig.runtime_fallback === "boolean"
+      ? { enabled: pluginConfig.runtime_fallback }
+      : pluginConfig.runtime_fallback
+
   const runtimeFallback = isHookEnabled("runtime-fallback")
     ? safeHook("runtime-fallback", () =>
         createRuntimeFallbackHook(ctx, {
-          config: pluginConfig.runtime_fallback,
+          config: runtimeFallbackConfig,
           pluginConfig,
         }))
     : null