fix: security and code quality improvements

Security fixes:
- Add file upload size limits (10MB) for customer and product imports
- Add XLSX file validation with row limits and magic byte checking
- Implement password validation (min 6 chars) in registration
- Add rate limiting for guest login (5 per IP per 15 minutes)
- Sanitize error messages to prevent information leakage
- Fix XSS vulnerability by removing unsafe v-html usage
- Enforce WhatsApp webhook signature verification
- Add SSRF protection with URL validation and IP blocking
- Fix marketing endpoints to use proper authentication

Code quality improvements:
- Create shared utility functions for UUID validation and string sanitization
- Remove duplicate UUID validation code from admin modules
- Remove dead code (pass statement in translation.py)
- Fix aliyun SDK import compatibility

backend/app/services/translation.py

@@ -50,9 +50,6 @@ class TranslationService:
         preference_context: Optional[str] = None,
     ) -> List[Dict[str, Any]]:
         similar = await self.corpus.find_similar(inquiry, "reply")
-        if similar and count > 1:
-            pass
-
         results = []
         tones = self._get_tones(tone, count)