feat(FN-1044): add thinkingLevel and planning model support to task creation

- Add thinkingLevel field to createTask and updateTask in core store
- Accept thinkingLevel and planningModel fields in dashboard task routes
- Send thinkingLevel and planningModel in frontend API calls from task forms
- Add ThinkingLevel selector to ModelSelectorTab component with tests
- Wire up planning model and thinking level in QuickEntryBox, TaskForm, and NewTaskModal
- Add unit tests for store, routes, and ModelSelectorTab coverage
- Add changeset and update AGENTS.md documentation

packages/cli/src/commands/dashboard.test.ts

@@ -219,6 +219,9 @@ vi.mock("@fusion/engine", async (importOriginal) => {
       start: vi.fn(),
       stop: vi.fn(),
     })),
+    createAiPromptExecutor: vi.fn().mockResolvedValue({
+      execute: vi.fn().mockResolvedValue(undefined),
+    }),
     SelfHealingManager: vi.fn().mockImplementation((_store: unknown, opts: unknown) => {
       capturedSelfHealingOpts = opts as Record<string, unknown>;
       return {