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/session.py

@@ -0,0 +1,14 @@
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class TradingSessionKey:
+    date: str
+    ticker: str | None = None
+
+    def __post_init__(self):
+        if not self.date:
+            raise ValueError("Session must have a date")
+
+    def key(self) -> str:
+        return f"{self.date}:{self.ticker or 'all'}"