feat: update login flow and add firework effects

- Update mobile HomeView to show WeChat scan login instructions
- Remove manual name/department input form from mobile client
- Add firework particle effects to big screen background
- Remove department field from login flow types

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

packages/server/src/app.ts

@@ -2,6 +2,7 @@ import express, { Application } from 'express';
 import cors from 'cors';
 import helmet from 'helmet';
 import compression from 'compression';
+import path from 'path';
 import { config } from './config';
 import { logger } from './utils/logger';
 import { errorHandler } from './middleware/errorHandler';
@@ -51,6 +52,9 @@ app.use(express.urlencoded({ extended: true }));
 // Request logging
 app.use(requestLogger);
 
+// Static files (for WeChat domain verification, etc.)
+app.use(express.static(path.join(__dirname, '../public')));
+
 // Health check
 app.get('/health', (_req, res) => {
   res.json({ status: 'ok', timestamp: new Date().toISOString() });