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/agents/AGENTS.md

@@ -2,7 +2,7 @@
 
 ## OVERVIEW
 
-10 AI agents for multi-model orchestration. Sisyphus (primary), oracle, librarian, explore, frontend, document-writer, multimodal-looker, Prometheus, Metis, Momus.
+8 AI agents for multi-model orchestration. Sisyphus (primary), oracle, librarian, explore, multimodal-looker, Prometheus, Metis, Momus.
 
 ## STRUCTURE
 
@@ -11,12 +11,10 @@ agents/
 ├── atlas.ts    # Orchestrator (1531 lines) - 7-phase delegation
 ├── sisyphus.ts                 # Main prompt (640 lines)
 ├── sisyphus-junior.ts          # Delegated task executor
-├── sisyphus-prompt-builder.ts  # Dynamic prompt generation
+├── dynamic-agent-prompt-builder.ts  # Dynamic prompt generation
 ├── oracle.ts                   # Strategic advisor (GPT-5.2)
 ├── librarian.ts                # Multi-repo research (GLM-4.7-free)
 ├── explore.ts                  # Fast grep (Grok Code)
-├── frontend-ui-ux-engineer.ts  # UI specialist (Gemini 3 Pro)
-├── document-writer.ts          # Technical writer (Gemini 3 Flash)
 ├── multimodal-looker.ts        # Media analyzer (Gemini 3 Flash)
 ├── prometheus-prompt.ts        # Planning (1196 lines) - interview mode
 ├── metis.ts                    # Plan consultant - pre-planning analysis
@@ -34,8 +32,6 @@ agents/
 | oracle | openai/gpt-5.2 | 0.1 | Read-only consultation, debugging |
 | librarian | opencode/glm-4.7-free | 0.1 | Docs, GitHub search, OSS examples |
 | explore | opencode/grok-code | 0.1 | Fast contextual grep |
-| frontend-ui-ux-engineer | google/gemini-3-pro-preview | 0.7 | UI generation, visual design |
-| document-writer | google/gemini-3-flash | 0.3 | Technical documentation |
 | multimodal-looker | google/gemini-3-flash | 0.1 | PDF/image analysis |
 | Prometheus | anthropic/claude-opus-4-5 | 0.1 | Strategic planning, interview mode |
 | Metis | anthropic/claude-sonnet-4-5 | 0.1 | Pre-planning gap analysis |