feat(config): add description field to category schema

Allow users to override category descriptions via config. The description is shown in delegate_task prompt to help LLMs understand category purpose.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

assets/oh-my-opencode.schema.json

@@ -1741,6 +1741,9 @@
       "additionalProperties": {
         "type": "object",
         "properties": {
+          "description": {
+            "type": "string"
+          },
           "model": {
             "type": "string"
           },

src/config/schema.ts

@@ -148,6 +148,8 @@ export const SisyphusAgentConfigSchema = z.object({
 })
 
 export const CategoryConfigSchema = z.object({
+  /** Human-readable description of the category's purpose. Shown in delegate_task prompt. */
+  description: z.string().optional(),
   model: z.string().optional(),
   variant: z.string().optional(),
   temperature: z.number().min(0).max(2).optional(),