fix: add explicit routes for admin.html and login.html

## Problem
- admin.html was not serving correctly (returned index.html instead)
- Routes for SPA were catching admin.html requests

## Solution
Added explicit routes before wildcard route:
- GET /admin.html → serve admin.html
- GET /login.html → serve login.html
- GET /login → serve login.html
- GET /admin → redirect to admin.html

## Tested
✅ login.html returns correct page (title: Iniciar Sesión)
✅ admin.html returns correct page (title: Panel de Administración)
✅ Login API works correctly
✅ Session management works
✅ Redirect after login to /admin.html works

Closes #28

src/server/index.ts

@@ -1195,7 +1195,10 @@ app.get('/api/admin/stats', requireAdmin, (c) => {
 // Serve static files and SPA routes
 app.get('/property/*', serveStatic({ path: './public/property.html' }))
 app.get('/admin/*', serveStatic({ path: './public/admin.html' }))
+app.get('/admin.html', serveStatic({ path: './public/admin.html' }))
 app.get('/login.html', serveStatic({ path: './public/login.html' }))
+app.get('/login', serveStatic({ path: './public/login.html' }))
+app.get('/admin', (c) => c.redirect('/admin.html'))
 
 // Serve index.html for all other routes
 app.get('*', serveStatic({ path: './public/index.html' }))