feat: cache canned responses and agents in IndexedDB

Converts the canned-response and agent API clients to CacheEnabledApiClient
subclasses and wires revalidate actions into the corresponding Vuex modules,
so settings pages and pickers stop fetching the same lists on every visit.
The canned-response search box continues to bypass the cache and hit the
network directly, so server-side ordering stays authoritative.

Also fixes a pre-existing gap in teams/revalidate: SET_TEAMS merges into a
record dict by id and never removes missing entries, so a team deleted
server-side would survive a reconnect-driven revalidate. Now matches the
get action by emitting CLEAR_TEAMS first.

Each affected spec clears its IDB store before every case, since the
preflight-throws-on-axios-reject pattern they relied on is going away in the
next commit.

app/javascript/dashboard/store/modules/specs/inboxes/actions.spec.js

@@ -1,12 +1,20 @@
 import axios from 'axios';
 import { actions } from '../../inboxes';
 import * as types from '../../../mutation-types';
+import InboxesAPI from '../../../../api/inboxes';
 import inboxList from './fixtures';
 
 const commit = vi.fn();
 global.axios = axios;
 vi.mock('axios');
 
+// Clear the IDB-backed cache between tests so each case starts from a known
+// empty state and isn't affected by data persisted by a previous test.
+beforeEach(async () => {
+  await InboxesAPI.dataManager.initDb();
+  await InboxesAPI.dataManager.db.clear(InboxesAPI.cacheModelName);
+});
+
 describe('#actions', () => {
   describe('#get', () => {
     it('sends correct actions if API is success', async () => {