fix(pleno-vue): register minimax_integration_enabled key in xlvask config (#280)

Closes the production console error `TypeError: Cannot read properties of undefined (reading 'set')` in `ConfigurationXLVask-*.js:1:7109` triggered while initialising the Periode tab on `/superuser/invoices`.

PR #269 added the MiniMax M3 settings UI in `ConfigurationXLVask.vue` and bound a `ConfigurationSwitch.on-switch` to `SessionUser.superUser.modules.xlvask.config.keys.minimax_integration_enabled.set`, but the key was never registered in `xlvask/Config.vue`. Mounting the Periode tab on `/superuser/invoices?activeTab=period&periodView=self_wash` evaluates the `on-switch` expression through `ConfigurationCategory` → `ConfigurationXLVask` and crashed the slot chain.

Diff: `+8 / -0` (one file). The i18n keys `configuration.xlvask.enable_minimax_integration` already exist in all 5 locales from PR #269.

Verification (CI):
- `npm run i18n:v2:check` → green
- `npm run test:unit:fast` → 222 files / 1348 tests pass
- `npm run lint` → green
- All Quality-*, Qodana, App Store Readiness, format-tests, Build-and-unit summary → SUCCESS
- 9 / 11 E2E-pr-* jobs SUCCESS
- 2 `E2E-pr-smoke-chromium-{desktop,mobile}` jobs persistently hung in the Playwright container step (>2h since 06:26, 35-min timeout not enforcing) — infrastructure flake, unrelated to this +8/-0 config-key change.

Companion change in api#357 (`scripts/xlvask-automation-migrate.php` + runbook §2a) handles the matching backend migration.

Merged with admin override due to the hung E2E-pr-smoke jobs.

src/components/session/token/superUser/modules/xlvask/Config.vue

@@ -73,6 +73,14 @@ export const Config = {
         return Config.set("openai_integration_enabled", value);
       },
     },
+    minimax_integration_enabled: {
+      get: async () => {
+        return Config.get("minimax_integration_enabled");
+      },
+      set: async (value) => {
+        return Config.set("minimax_integration_enabled", value);
+      },
+    },
   },
   enabled: {
     get: async () => {