Add password validation with i18n support and GitHub button improvements

- Add password field to UserUpdate schema for password change on edit
- Implement password validation in update_user endpoint
- Add i18n translations for password validation errors (ru/en)
- Update SecurityService.validate_password to support language parameter
- Add GitHub icon and repository name 'pvemanager' to header button
- Fix internal server error when updating user password
- Clean up hardcoded translations in frontend

backend/app/api/auth.py

@@ -317,7 +317,8 @@ def register_user(
         )
     
     # Validate password
-    is_valid, errors = SecurityService.validate_password(db, user_data.password)
+    lang = request.cookies.get("language", "en")
+    is_valid, errors = SecurityService.validate_password(db, user_data.password, lang)
     if not is_valid:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
@@ -446,7 +447,8 @@ def change_password(
         )
     
     # Validate new password
-    is_valid, errors = SecurityService.validate_password(db, new_password)
+    lang = request.cookies.get("language", "en")
+    is_valid, errors = SecurityService.validate_password(db, new_password, lang)
     if not is_valid:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,