fix(pos): corregir error 'state is not defined' y favicon 404

- catalog.js: state → nav (variable correcta del catalogo)
- vsClearAll: resetea nav en vez de state inexistente
- favicon.ico: sirve icon-192.png del PWA

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/app.py

@@ -52,6 +52,10 @@ def create_app():
 
     from flask import render_template, send_from_directory, jsonify, g
 
+    @app.route('/favicon.ico')
+    def favicon():
+        return send_from_directory('static/pwa', 'icon-192.png', mimetype='image/png')
+
     @app.route('/pos/login')
     def pos_login():
         return render_template('login.html',