feat: WeChat Pay integration, translation quota management, login UX fixes

- WeChat Pay APIv3 integration (JSAPI + Native) with cert-based auth
- TranslationQuota model + admin management UI (配额 tab)
- Alibaba MT provider now checks quota before translation
- Fix: admin tabs scrollable on mobile, remove header-card
- Fix: profile/login navigation - logout stays on profile, login returns to profile
- Fix: login form now visible by default (no extra click to show)
- Fix: home page translate link uses navigateTo (was switchTab to non-tabBar page)
- Add .coverage and apiclient_key.pem to gitignore

backend/app/api/v1/admin.py

@@ -5,6 +5,7 @@ from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.ext.asyncio import AsyncSession
 from app.database import get_db
 from app.services.admin import AdminService
+from app.services.translation_quota import TranslationQuotaService
 from app.api.v1.deps import get_current_user
 
 router = APIRouter()
@@ -173,3 +174,41 @@ async def system_health(
 ):
     service = AdminService(db)
     return await service.get_system_health()
+
+
+@router.get("/translation-quotas")
+async def list_translation_quotas(
+    _: dict = Depends(require_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    service = TranslationQuotaService(db)
+    return await service.get_all_quotas()
+
+
+@router.put("/translation-quotas/{version}")
+async def update_translation_quota(
+    version: str,
+    data: dict,
+    _: dict = Depends(require_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    allowed = {"monthly_limit", "enabled", "description"}
+    filtered = {k: v for k, v in data.items() if k in allowed}
+    service = TranslationQuotaService(db)
+    result = await service.update_quota(version, filtered)
+    if not result:
+        raise HTTPException(status_code=404, detail="Quota not found")
+    return result
+
+
+@router.post("/translation-quotas/{version}/reset")
+async def reset_translation_quota(
+    version: str,
+    _: dict = Depends(require_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    service = TranslationQuotaService(db)
+    result = await service.reset_usage(version)
+    if not result:
+        raise HTTPException(status_code=404, detail="Quota not found")
+    return result