refactor(agents): remove document-writer agent in favor of writing category

- Delete document-writer.ts agent file
- Remove from types, schema, utils, index exports
- Remove tool restrictions entry
- Remove migration mappings
- Update atlas.ts to use category="writing" instead of agent="document-writer"
- Update init-deep command template
- Update all documentation (AGENTS.md, README.*, docs/)
- Regenerate schema.json

document-writer functionality is now handled via delegate_task with
category="writing" which uses the writing category's model config.

src/shared/agent-tool-restrictions.ts

@@ -28,18 +28,6 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
     read: true,
   },
 
-  "document-writer": {
-    task: false,
-    delegate_task: false,
-    call_omo_agent: false,
-  },
-
-  "frontend-ui-ux-engineer": {
-    task: false,
-    delegate_task: false,
-    call_omo_agent: false,
-  },
-
   "Sisyphus-Junior": {
     task: false,
     delegate_task: false,