feat(KB-617): add diff viewer tab to task detail modal

- Add modifiedFiles and baseCommitSha tracking during task execution
- Create GET /tasks/:id/diff API endpoint for file list and patches
- Build TaskChangesTab component with expandable file diffs
- Integrate Changes tab into TaskDetailModal for in-progress, in-review, and done tasks
- Add database columns and types for diff tracking
- Update executor to capture modified files during agent sessions

packages/cli/src/commands/task.ts

@@ -1423,7 +1423,7 @@ export async function runTaskPlan(initialPlanArg?: string, yesFlag = false, proj
 
       try {
         showThinking();
-        result = await submitResponse(sessionId, response) as typeof result;
+        result = await submitResponse(sessionId, response as Record<string, unknown>) as typeof result;
         clearThinking();
       } catch (err) {
         clearThinking();