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/runtime/registry.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from typing import Dict, Optional
+
+
+class RuntimeRegistry:
+    def __init__(self) -> None:
+        self._states: Dict[str, "AgentRuntimeState"] = {}
+
+    def register(self, agent_id: str, state: "AgentRuntimeState") -> None:
+        self._states[agent_id] = state
+
+    def get(self, agent_id: str) -> Optional["AgentRuntimeState"]:
+        return self._states.get(agent_id)
+
+    def list_agents(self) -> list[str]:
+        return list(self._states.keys())
+
+    def clear(self) -> None:
+        self._states.clear()