feat: API key management improvements

- Rename routes: /dashboard/tokens → /dashboard/apikeys, /dashboard/manager/keys → /dashboard/manager/channels
- Add KeyPlain field to store plaintext API keys for re-viewing
- API key list shows masked key (sk-ot-123456****abcd) with eye toggle to reveal
- Copy button with 2s feedback on key list
- TokenNew shows full key + copy after creation
- Increase key prefix display to 12 characters
- Fix SQLite driver: replace gorm.io/driver/sqlite with ncruces/go-sqlite3/gormlite
- Fix user.status === 'active' checks across frontend views
- Add channel store for new channels API
- Update Makefile frontend build to work reliably

BREAKING CHANGE: Existing API keys created before this change will not show their plaintext value (only prefix visible).

frontend/src/views/dashboard/Overview.vue

@@ -63,8 +63,8 @@
                             <dt class="shrink-0 text-base-content/60">状态</dt>
                             <dd>
                                 <span class="badge badge-sm"
-                                    :class="user?.active ? 'badge-success badge-soft' : 'badge-error badge-soft'">
-                                    {{ user?.active ? 'Active' : 'Inactive' }}
+                                    :class="user?.status === 'active' ? 'badge-success badge-soft' : 'badge-error badge-soft'">
+                                    {{ user?.status === 'active' ? 'Active' : 'Inactive' }}
                                 </span>
                             </dd>
                         </div>