fix: project-scope terminal, file browser, agent execution, and heartbeat monitor

- TerminalService: use per-project instance map instead of destructive singleton
- File browser: thread projectId through API functions, hooks, and components
- Workspace file editor: pass projectId to read/write operations
- Agent heartbeat: guard execution with project scope validation
- Agent runs/stop: validate heartbeatMonitor matches scoped project
- CLI dashboard/serve: pass rootDir to heartbeatMonitor via server options
- Add getRootDir() to HeartbeatMonitor for scope comparison

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

packages/dashboard/src/server.ts

@@ -109,6 +109,8 @@ export interface ServerOptions {
   };
   /** Optional HeartbeatMonitor for triggering agent execution runs */
   heartbeatMonitor?: {
+    /** Project root directory this monitor is bound to. Used for scope validation. */
+    rootDir?: string;
     startRun(agentId: string, options?: { source: import("@fusion/core").HeartbeatInvocationSource; triggerDetail?: string; contextSnapshot?: Record<string, unknown> }): Promise<import("@fusion/core").AgentHeartbeatRun>;
     executeHeartbeat(options: {
       agentId: string;