feat: Add agent workspace system and runtime management

- Add agent core modules (agent_core, factory, registry, skill_loader)
- Add runtime system for agent execution management
- Add REST API for agents, workspaces, and runtime control
- Add process supervisor for agent lifecycle management
- Add workspace template system with agent profiles
- Add frontend RuntimeView and runtime API integration
- Add per-agent skill workspaces for smoke_fullstack run
- Refactor skill system with active/installed separation

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

backend/workspaces/.template/agent.yaml

@@ -0,0 +1,10 @@
+agent_id: {{agent_id}}
+agent_type: {{agent_type}}
+name: {{name}}
+model:
+  provider: openai
+  model_name: gpt-4o
+  temperature: 0.3
+enabled_skills: []
+disabled_skills: []
+settings: {}