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/search_web.py

@@ -56,6 +56,31 @@ async def _google_cse(query: str, max_results: int, api_key: str, cse_id: str) -
 
 
 async def fetch_page_text(url: str) -> Optional[str]:
+    # Validate URL to prevent SSRF
+    from urllib.parse import urlparse
+    import ipaddress
+    
+    try:
+        parsed = urlparse(url)
+        if parsed.scheme not in ('http', 'https'):
+            logger.warning(f"Invalid URL scheme: {url}")
+            return None
+        
+        # Check if hostname is an IP address and block private/reserved ranges
+        hostname = parsed.hostname
+        if hostname:
+            try:
+                ip = ipaddress.ip_address(hostname)
+                if ip.is_private or ip.is_loopback or ip.is_reserved or ip.is_link_local:
+                    logger.warning(f"Blocked private/reserved IP: {url}")
+                    return None
+            except ValueError:
+                # Not an IP address, it's a hostname - proceed normally
+                pass
+    except Exception as e:
+        logger.warning(f"URL validation failed for {url}: {e}")
+        return None
+    
     try:
         async with httpx.AsyncClient(timeout=10.0, follow_redirects=True) as client:
             resp = await client.get(url, headers={"User-Agent": "Mozilla/5.0"})