feat(agents): add category and display fields to AgentType model

Add 6 new fields to AgentType for better organization and UI display:
- category: enum for grouping (development, design, quality, etc.)
- icon: Lucide icon identifier for UI
- color: hex color code for visual distinction
- sort_order: display ordering within categories
- typical_tasks: list of tasks the agent excels at
- collaboration_hints: agent slugs that work well together

Backend changes:
- Add AgentTypeCategory enum to enums.py
- Update AgentType model with 6 new columns and indexes
- Update schemas with validators for new fields
- Add category filter and /grouped endpoint to routes
- Update CRUD with get_grouped_by_category method
- Update seed data with categories for all 27 agents
- Add migration 0007

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/init_db.py

@@ -149,6 +149,13 @@ async def load_default_agent_types(session: AsyncSession) -> None:
                 mcp_servers=agent_type_data.get("mcp_servers", []),
                 tool_permissions=agent_type_data.get("tool_permissions", {}),
                 is_active=agent_type_data.get("is_active", True),
+                # Category and display fields
+                category=agent_type_data.get("category"),
+                icon=agent_type_data.get("icon", "bot"),
+                color=agent_type_data.get("color", "#3B82F6"),
+                sort_order=agent_type_data.get("sort_order", 0),
+                typical_tasks=agent_type_data.get("typical_tasks", []),
+                collaboration_hints=agent_type_data.get("collaboration_hints", []),
             )
 
             await agent_type_crud.create(session, obj_in=agent_type_in)