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>

gui/login_dialog.py

@@ -1,6 +1,7 @@
 """
 Login Dialog - Modal dialog for user authentication
 """
+import socket
 import tkinter as tk
 from tkinter import ttk, messagebox
 from typing import Optional, Tuple
@@ -37,7 +38,7 @@ class LoginDialog:
         """Create the login dialog UI"""
         self.dialog = tk.Toplevel(self.parent)
         self.dialog.title("ERP 自动化工具 - 登录")
-        self.dialog.geometry("400x250")
+        self.dialog.geometry("400x280")
         self.dialog.resizable(False, False)
 
         # Center the dialog on parent
@@ -52,7 +53,7 @@ class LoginDialog:
         parent_height = self.parent.winfo_height()
 
         dialog_width = 400
-        dialog_height = 250
+        dialog_height = 280
         x = parent_x + (parent_width - dialog_width) // 2
         y = parent_y + (parent_height - dialog_height) // 2
         self.dialog.geometry(f"{dialog_width}x{dialog_height}+{x}+{y}")
@@ -78,7 +79,16 @@ class LoginDialog:
             text="请登录",
             font=('', 16, 'bold')
         )
-        title_label.pack(pady=(0, 20))
+        title_label.pack(pady=(0, 10))
+
+        # Computer name display
+        computer_name_label = ttk.Label(
+            main_frame,
+            text=f"当前计算机: {socket.gethostname()}",
+            font=('', 9),
+            foreground='gray'
+        )
+        computer_name_label.pack(pady=(0, 15))
 
         # Username field
         username_frame = ttk.Frame(main_frame)