新增：管理后台前端页面，以及openspec内容。

openspec/changes/add-admin-web/proposal.md

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+# Change: Implement Admin Web Management System
+
+## Why
+The project needs a web-based administrative interface to manage users and conversation records from the WeChat mini-program. Currently, there is no centralized way for administrators to view, search, and manage system data.
+
+## What Changes
+- Implement a complete admin web application using Vue 3.x + Element Plus + Vite
+- Create user management page with search and pagination
+- Create conversation record management page with filtering capabilities
+- Implement authentication system with login page
+- Add responsive layout with sidebar navigation
+- Implement dark/light theme switching
+- Set up routing with vue-router
+- Configure state management with Pinia
+- Set up HTTP client with axios and interceptors
+
+## Impact
+- Affected specs: backend-admin
+- Affected code: admin-web/ (new directory)
+- Dependencies: Vue 3.x, Element Plus, Vite, vue-router, Pinia, axios