feat: add computer name-based silent login (无感登录)

Implement automatic authentication based on computer name to enable
passwordless login for registered computers with fallback to manual
authentication.

Changes:
- Add SessionManager.login_by_computer_name() for silent login attempt
- Add BIPUsersDAO.authenticate_by_computer_name() for computer name lookup
- Update BIPUsersDAO.create_user() to support optional computer_name parameter
- Update main_ui.py to try silent login before showing login dialog
- Display current computer name in login dialog for user reference

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

auth/session_manager.py

@@ -63,6 +63,28 @@ class SessionManager:
             return True
         return False
 
+    def login_by_computer_name(self) -> bool:
+        """
+        Attempt silent login using computer name
+
+        Returns:
+            True if login successful, False otherwise
+        """
+        import socket
+        from db.bip_users_dao import BIPUsersDAO
+
+        computer_name = socket.gethostname()
+        dao = BIPUsersDAO()
+        user_info = dao.authenticate_by_computer_name(computer_name)
+
+        if user_info:
+            self._current_user = {
+                'username': user_info['username'],
+                'user_type': user_info['user_type']
+            }
+            return True
+        return False
+
     def logout(self):
         """Logout the current user and clear session"""
         self._current_user = None