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/schemas.py

@@ -22,6 +22,9 @@ class UserUpdate(BaseModel):
     full_name: Optional[str] = Field(None, max_length=100)
     password: Optional[str] = Field(None, min_length=6, max_length=100)
     is_active: Optional[bool] = None
+    is_admin: Optional[bool] = None
+    role_id: Optional[int] = None
+    require_password_change: Optional[bool] = None
 
 
 class UserResponse(UserBase):