fix(gateway): 이벤트 기수 0 저장을 허용

숫자 입력에서 Vue가 반환한 number 값을 안전하게 정규화해 다음 시즌 번호 0이 메타 저장 요청까지 전달되도록 수정한다. API 경계와 실제 Chromium payload 회귀 테스트를 추가한다.

app/gateway-api/test/adminOperations.test.ts

@@ -789,6 +789,30 @@ describe('admin operation API', () => {
         ).rejects.toBeDefined();
     });
 
+    it('stores event season zero as the next season number', async () => {
+        const harness = await buildCaller(
+            async () => {
+                throw new Error('not used');
+            },
+            { adminRoles: ['admin.profiles.settings:che:2'], firstUserIsAdmin: false }
+        );
+
+        await harness.caller.admin.profiles.updateMeta({
+            profileName: 'che:2',
+            patch: { nextSeasonIdx: 0 },
+            reason: 'prepare event season',
+        });
+        expect(harness.updatedMetas.at(-1)).toMatchObject({ nextSeasonIdx: 0 });
+
+        await expect(
+            harness.caller.admin.profiles.updateMeta({
+                profileName: 'che:2',
+                patch: { nextSeasonIdx: -1 },
+                reason: 'reject negative season',
+            })
+        ).rejects.toBeDefined();
+    });
+
     it('does not let a scenario-only operator combine a Git update with reset', async () => {
         const harness = await buildCaller(
             async () => {

app/gateway-frontend/e2e/server-operations.spec.ts

@@ -1040,6 +1040,33 @@ test('edits server reset defaults through profile metadata settings', async ({ p
     expect(request).toContain('"npcMode":2');
 });
 
+test('stores event season zero from server metadata settings', async ({ page }) => {
+    const state: FixtureState = { operations: [], gatewayOperations: [], runtimeRunning: true, requestBodies: [] };
+    await installFixture(page, state);
+
+    await page.goto('admin/servers/che%3Adefault');
+    const nextSeasonInput = page.getByTestId('next-season-idx');
+    await nextSeasonInput.fill('0');
+    await expect(nextSeasonInput).toHaveValue('0');
+    expect(
+        await nextSeasonInput.evaluate((element: HTMLInputElement) => ({
+            valid: element.validity.valid,
+            valueAsNumber: element.valueAsNumber,
+        }))
+    ).toEqual({ valid: true, valueAsNumber: 0 });
+    await page.getByPlaceholder('변경 사유 (필수)').fill('prepare event season');
+    await page.getByRole('button', { name: '메타 저장' }).click();
+
+    await expect
+        .poll(() => state.requestBodies.find((entry) => entry.operation === 'admin.profiles.updateMeta'))
+        .toBeTruthy();
+    const request = JSON.stringify(
+        state.requestBodies.find((entry) => entry.operation === 'admin.profiles.updateMeta')?.body
+    );
+    expect(request).toContain('"nextSeasonIdx":0');
+    await expect(page.getByTestId('action-toast').filter({ hasText: '메타 저장 완료' })).toBeVisible();
+});
+
 test('shows a dismissible error toast when profile metadata persistence fails', async ({ page }, testInfo) => {
     const state: FixtureState = {
         operations: [],

app/gateway-frontend/src/views/AdminView.vue

@@ -407,7 +407,7 @@ const profileEdits = ref<
             color: string;
             inGameNotice: string;
             profileImageUrl: string;
-            nextSeasonIdx: string;
+            nextSeasonIdx: string | number;
             localAccountAccessGraceDays: string;
             localAccountGeneralCreationGraceDays: string;
             resetDefaults: ProfileResetDefaults;
@@ -770,7 +770,10 @@ const updateProfileMeta = async (profileName: string) => {
     if (!edit) {
         return;
     }
-    const nextSeasonRaw = edit.nextSeasonIdx.trim();
+    // Vue casts non-empty values from type="number" inputs to numbers even when
+    // the buffer was initialized with a string. Normalize both runtime shapes so
+    // event season 0 reaches the metadata mutation instead of throwing on trim().
+    const nextSeasonRaw = String(edit.nextSeasonIdx).trim();
     const nextSeasonIdx = nextSeasonRaw === '' ? null : Number(nextSeasonRaw);
     if (nextSeasonIdx !== null && (!Number.isFinite(nextSeasonIdx) || nextSeasonIdx < 0)) {
         profileActionStatus.value = {
@@ -2229,6 +2232,7 @@ onMounted(() => {
                                         type="number"
                                         min="0"
                                         step="1"
+                                        data-testid="next-season-idx"
                                         class="w-full bg-zinc-950 border border-zinc-700 rounded px-3 py-2 text-sm text-white"
                                         placeholder="예: 12"
                                     />