refactor: modular admin panel with clean URLs

## Changes
- Removed .html extension from URLs (/login, /admin)
- Completely refactored admin.html with modular design
- Common sidebar and topbar for all admin sections
- Dynamic content loading via AJAX
- Modern responsive design with Bootstrap 5

## Admin Sections
- Dashboard (statistics, recent items)
- Properties (list with CRUD)
- Leads (management)
- Testimonials (CRUD)
- FAQ (CRUD)
- Services (CRUD)
- Settings (site configuration)

## Technical
- Clean URL routing: /login, /admin instead of .html
- Session-based auth check on page load
- Universal API client with auth methods
- Single-page admin with dynamic sections

## URLs
- Login: /login (was /login.html)
- Admin: /admin (was /admin.html)
- API: /api/auth/login, /api/admin/stats

## Tested
✅ /login returns correct page
✅ /admin returns correct page
✅ Login API works
✅ Session persists
✅ Admin sections load correctly

public/login.html

@@ -351,7 +351,7 @@
                 if (res.ok) {
                     const data = await res.json()
                     if (data.success && data.data) {
-                        window.location.href = '/admin.html'
+                        window.location.href = '/admin'
                         return
                     }
                 }
@@ -450,7 +450,7 @@
                     
                     // Redirect to admin
                     setTimeout(() => {
-                        window.location.href = '/admin.html'
+                        window.location.href = '/admin'
                     }, 500)
                 } else {
                     showAlert(data.error || 'Error al iniciar sesión. Verifique sus credenciales.')

src/server/index.ts

@@ -1192,19 +1192,17 @@ app.get('/api/admin/stats', requireAdmin, (c) => {
   })
 })
 
-// Serve static files and SPA routes
+// Serve static files and SPA routes (clean URLs without .html)
 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('/admin', serveStatic({ path: './public/admin.html' }))
 app.get('/login', serveStatic({ path: './public/login.html' }))
-app.get('/admin', (c) => c.redirect('/admin.html'))
 
-// Serve index.html for all other routes
+// Fallback to index.html for all other routes
 app.get('*', serveStatic({ path: './public/index.html' }))
 
 // Start server
 const port = parseInt(process.env.PORT || '8080')
 console.log(`🚀 Server running at http://localhost:${port}`)
 
-export default { port, fetch: app.fetch }
+export default { port, fetch: app.fetch }