feat(agent): add agent management UI, skills/tools/triggers, and issue assignment

- Complete agents management page with create dialog, runtime device selector,
  skills/tools/triggers/tasks tabs, and agent detail view
- Add AssigneePicker to issue detail page for assigning to members or agents
- Extend agent types with description, skills, tools, triggers, RuntimeDevice
- Add SDK methods for agent CRUD and task listing
- Add migration 002 for agent config columns (skills, tools, triggers)
- Update seed data with realistic agent configurations
- Use auth context as single source of truth for agents (fixes state sync)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/migrations/002_agent_config.down.sql

@@ -0,0 +1,5 @@
+ALTER TABLE agent
+    DROP COLUMN IF EXISTS description,
+    DROP COLUMN IF EXISTS skills,
+    DROP COLUMN IF EXISTS tools,
+    DROP COLUMN IF EXISTS triggers;