fix(monitor): ignore stale template picker responses

[ouchihao]

Closing the apply picker and opening another template while its list request is pending can let the older response replace the current monitor list and selection. Track the request version so only the current request updates the list, errors and loading state; invalidate pending requests on close or unmount.

Validation:

• Covers reversed responses and the resulting apply payload, stale failures during loading, close/unmount, and current-request errors. 4 regression cases fail before the fix; all 5 focused cases pass after it.
• Focused tests plus the 17 Makefile critical frontend suites: 232 tests passed.
• vue-tsc --noEmit, full frontend ESLint and git diff --check passed.

Validation uses component tests with mocked APIs; no live server testing.