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/ai/router.py

@@ -1,6 +1,6 @@
 from typing import Dict, Any, Optional, List
 from app.ai.base import AIProvider
-from app.ai.providers import OpenAIProvider, ClaudeProvider, DeepLProvider, LocalProvider, SparkProvider, SensenovaProvider, OpencodeGoProvider, NvidiaProvider
+from app.ai.providers import OpenAIProvider, ClaudeProvider, DeepLProvider, LocalProvider, SparkProvider, SensenovaProvider, OpencodeGoProvider, NvidiaProvider, AlibabaMTProvider
 from app.config import settings
 from app.ai.trade_corpus import TradeCorpus
 import logging
@@ -81,6 +81,16 @@ class AIRouter:
             except Exception as e:
                 logger.warning(f"Spark init failed: {e}")
 
+        if settings.ALIBABA_ACCESS_KEY_ID and settings.ALIBABA_ACCESS_KEY_SECRET:
+            try:
+                self.providers["alibaba-mt"] = AlibabaMTProvider(
+                    access_key_id=settings.ALIBABA_ACCESS_KEY_ID,
+                    access_key_secret=settings.ALIBABA_ACCESS_KEY_SECRET,
+                )
+                logger.info("Alibaba MT provider ready")
+            except Exception as e:
+                logger.warning(f"Alibaba MT init failed: {e}")
+
         if settings.LOCAL_MODEL_ENABLED:
             try:
                 self.providers["local"] = LocalProvider(model_url=settings.LOCAL_MODEL_URL)