fix(delegate-task): category default model takes precedence over parent model

Previously, parent model string would override category default model,
causing categories like 'ultrabrain' to use the parent's model (e.g., sonnet)
instead of the intended category default (e.g., gpt-5.2).

Model priority is now:
1. userConfig.model (oh-my-opencode.json override)
2. defaultConfig.model (category default)
3. parentModelString (fallback)
4. systemDefaultModel (last resort)

src/tools/delegate-task/tools.ts

@@ -124,9 +124,8 @@ function resolveCategoryConfig(
     return null
   }
 
-  // Model priority: user override > parent model (inherit) > category default > system default
-  // Parent model takes precedence over category default so custom providers work out-of-box
-  const model = userConfig?.model ?? parentModelString ?? defaultConfig?.model ?? systemDefaultModel
+  // Model priority: user override > category default > parent model (fallback) > system default
+  const model = userConfig?.model ?? defaultConfig?.model ?? parentModelString ?? systemDefaultModel
   const config: CategoryConfig = {
     ...defaultConfig,
     ...userConfig,