feat(KB-616): add ProjectRuntime abstraction for task execution isolation

- Define ProjectRuntime interface with unified task execution contract\n- Implement IPC protocol for host-worker communication (messages, streaming, heartbeats)\n- Add InProcessRuntime for synchronous in-process task execution\n- Add ChildProcessRuntime with isolated worker processes for sandboxed execution\n- Implement ProjectManager to coordinate runtime selection and task lifecycle\n- Update engine exports to expose runtime APIs\n- Add comprehensive tests for all runtime implementations and IPC protocol

packages/engine/src/logger.ts

@@ -64,3 +64,12 @@ export const reviewerLog = createLogger("reviewer");
 
 /** Logger for the PR monitor subsystem. */
 export const prMonitorLog = createLogger("pr-monitor");
+
+/** Logger for the project runtime subsystem. */
+export const runtimeLog = createLogger("runtime");
+
+/** Logger for the IPC subsystem. */
+export const ipcLog = createLogger("ipc");
+
+/** Logger for the project manager subsystem. */
+export const projectManagerLog = createLogger("project-manager");