refactor: migrate wechat to user attributes and enhance users list

Migrate the hardcoded wechat field to the new extensible user
attributes system and improve the users management UI.

Migration:
- Add migration 019 to move wechat data to user_attribute_values
- Remove wechat field from User entity, DTOs, and API contracts
- Clean up wechat-related code from backend and frontend

UsersView enhancements:
- Add text labels to action buttons (Filter Settings, Column Settings,
  Attributes Config) for better UX
- Change status column to show colored dot + Chinese text instead of
  English text
- Add dynamic attribute columns support with batch loading
- Add column visibility settings with localStorage persistence
- Add filter settings modal for search and filter preferences
- Update i18n translations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/views/user/ProfileView.vue

@@ -89,25 +89,6 @@
               </svg>
               <span class="truncate">{{ user.username }}</span>
             </div>
-            <div
-              v-if="user?.wechat"
-              class="flex items-center gap-3 text-sm text-gray-600 dark:text-gray-400"
-            >
-              <svg
-                class="h-4 w-4 text-gray-400 dark:text-gray-500"
-                fill="none"
-                viewBox="0 0 24 24"
-                stroke="currentColor"
-                stroke-width="1.5"
-              >
-                <path
-                  stroke-linecap="round"
-                  stroke-linejoin="round"
-                  d="M8.625 12a.375.375 0 11-.75 0 .375.375 0 01.75 0zm0 0H8.25m4.125 0a.375.375 0 11-.75 0 .375.375 0 01.75 0zm0 0H12m4.125 0a.375.375 0 11-.75 0 .375.375 0 01.75 0zm0 0h-.375M21 12c0 4.556-4.03 8.25-9 8.25a9.764 9.764 0 01-2.555-.337A5.972 5.972 0 015.41 20.97a5.969 5.969 0 01-.474-.065 4.48 4.48 0 00.978-2.025c.09-.457-.133-.901-.467-1.226C3.93 16.178 3 14.189 3 12c0-4.556 4.03-8.25 9-8.25s9 3.694 9 8.25z"
-                />
-              </svg>
-              <span class="truncate">{{ user.wechat }}</span>
-            </div>
           </div>
         </div>
       </div>
@@ -170,19 +151,6 @@
               />
             </div>
 
-            <div>
-              <label for="wechat" class="input-label">
-                {{ t('profile.wechat') }}
-              </label>
-              <input
-                id="wechat"
-                v-model="profileForm.wechat"
-                type="text"
-                class="input"
-                :placeholder="t('profile.enterWechat')"
-              />
-            </div>
-
             <div class="flex justify-end pt-4">
               <button type="submit" :disabled="updatingProfile" class="btn btn-primary">
                 {{ updatingProfile ? t('profile.updating') : t('profile.updateProfile') }}
@@ -338,8 +306,7 @@ const passwordForm = ref({
 })
 
 const profileForm = ref({
-  username: '',
-  wechat: ''
+  username: ''
 })
 
 const changingPassword = ref(false)
@@ -354,7 +321,6 @@ onMounted(async () => {
     // Initialize profile form with current user data
     if (user.value) {
       profileForm.value.username = user.value.username || ''
-      profileForm.value.wechat = user.value.wechat || ''
     }
   } catch (error) {
     console.error('Failed to load contact info:', error)
@@ -407,8 +373,7 @@ const handleUpdateProfile = async () => {
   updatingProfile.value = true
   try {
     const updatedUser = await userAPI.updateProfile({
-      username: profileForm.value.username,
-      wechat: profileForm.value.wechat
+      username: profileForm.value.username
     })
 
     // Update auth store with new user data