feat: add admin user management with role-based access and self-protection

- Add AdminRequired middleware for admin-role routes
- Add login status check to reject disabled/locked accounts
- Add CRUD handlers (list, create, edit, delete) for users
- Add user_list and user_form templates with role/status badges
- Add nav entry and dashboard button for user management
- Add dynamic user count on admin dashboard
- Fix userIDFromSession to handle all numeric session types
- Self-protection: cannot delete/disable self or demote last admin
- Add EN/ZH i18n keys for all user management strings

i18n/i18n.go

@@ -269,6 +269,48 @@ var translations = map[Lang]map[string]string{
 		"comment_settings_guest_approval": "Require approval for guest comments",
 		"comment_settings_use_gravatar":   "Use Gravatar avatars",
 		"comment_settings_use_gravatar_hint": "When off, avatars show the author's initial on a colored background.",
+
+		// Admin: user management
+		"admin_users":               "Users",
+		"admin_users_title":         "Users",
+		"user_list_title":           "User Management",
+		"user_new":                  "New User",
+		"user_create_title":         "Create User",
+		"user_edit_title":           "Edit User",
+		"user_col_username":         "Username",
+		"user_col_display":          "Display Name",
+		"user_col_email":            "Email",
+		"user_col_role":             "Role",
+		"user_col_status":           "Status",
+		"user_col_created":          "Created",
+		"user_col_actions":          "Actions",
+		"user_username":             "Username",
+		"user_password":             "Password",
+		"user_password_hint":        "Leave blank to keep the current password.",
+		"user_display_name":         "Display Name",
+		"user_email":                "Email",
+		"user_gender":               "Gender",
+		"user_birthday":             "Birthday",
+		"user_role":                 "Role",
+		"user_status":               "Status",
+		"role_admin":                "Admin",
+		"role_author":               "Author",
+		"status_normal":             "Normal",
+		"status_disabled":           "Disabled",
+		"status_locked":             "Locked",
+		"status_unactivated":        "Unactivated",
+		"user_created":              "User created.",
+		"user_updated":              "User updated.",
+		"user_deleted":              "User deleted.",
+		"user_delete_confirm":       "Delete this user?",
+		"user_empty":                "No users.",
+		"user_username_required":    "Username is required.",
+		"user_password_required":    "Password is required.",
+		"user_username_exists":      "Username already exists.",
+		"user_cannot_delete_self":   "You cannot delete your own account.",
+		"user_cannot_disable_self":  "You cannot disable or lock your own account.",
+		"user_cannot_remove_last_admin": "Cannot remove the last administrator.",
+		"dash_user_mgmt":            "Manage Users",
 	},
 	ZH: {
 		// 导航
@@ -523,6 +565,48 @@ var translations = map[Lang]map[string]string{
 		"comment_settings_guest_approval": "非登录用户评论需审核",
 		"comment_settings_use_gravatar":   "使用 Gravatar 头像",
 		"comment_settings_use_gravatar_hint": "关闭后，头像将显示作者名称首字母的彩色占位。",
+
+		// 后台：用户管理
+		"admin_users":               "用户",
+		"admin_users_title":         "用户",
+		"user_list_title":           "用户管理",
+		"user_new":                  "新建用户",
+		"user_create_title":         "新建用户",
+		"user_edit_title":           "编辑用户",
+		"user_col_username":         "用户名",
+		"user_col_display":          "显示名称",
+		"user_col_email":            "邮箱",
+		"user_col_role":             "角色",
+		"user_col_status":           "状态",
+		"user_col_created":          "创建时间",
+		"user_col_actions":          "操作",
+		"user_username":             "用户名",
+		"user_password":             "密码",
+		"user_password_hint":        "留空则保持原密码不变。",
+		"user_display_name":         "显示名称",
+		"user_email":                "邮箱",
+		"user_gender":               "性别",
+		"user_birthday":             "生日",
+		"user_role":                 "角色",
+		"user_status":               "状态",
+		"role_admin":                "管理员",
+		"role_author":               "作者",
+		"status_normal":             "正常",
+		"status_disabled":           "禁用",
+		"status_locked":             "锁定",
+		"status_unactivated":        "未激活",
+		"user_created":              "用户已创建。",
+		"user_updated":              "用户已更新。",
+		"user_deleted":              "用户已删除。",
+		"user_delete_confirm":       "确认删除该用户？",
+		"user_empty":                "暂无用户。",
+		"user_username_required":    "请填写用户名。",
+		"user_password_required":    "请填写密码。",
+		"user_username_exists":      "用户名已存在。",
+		"user_cannot_delete_self":   "不能删除自己的账号。",
+		"user_cannot_disable_self":  "不能禁用或锁定自己的账号。",
+		"user_cannot_remove_last_admin": "不能移除最后一个管理员。",
+		"dash_user_mgmt":            "用户管理",
 	},
 }