fix(sw): v6 with network-first HTML strategy

- Bump cache to nexus-pos-v6 to force invalidation
- HTML pages now use network-first instead of cache-first
  This ensures users always get the latest HTML with correct
  JS/CSS references (?v=3) instead of stale cached HTML
- Remove HTML pages from APP_SHELL precache (only static assets)
- Keep cache-first for JS/CSS/images

pos/static/pwa/sw.js

@@ -1,20 +1,10 @@
 // /home/Autopartes/pos/static/pwa/sw.js
-// Nexus POS — Service Worker v5
+// Nexus POS — Service Worker v6
 // Self-contained vanilla JS. No external imports.
 
-const CACHE_NAME = 'nexus-pos-v5';
+const CACHE_NAME = 'nexus-pos-v6';
 
 const APP_SHELL = [
-  '/pos/login',
-  '/pos/sale',
-  '/pos/catalog',
-  '/pos/inventory',
-  '/pos/customers',
-  '/pos/invoicing',
-  '/pos/accounting',
-  '/pos/dashboard',
-  '/pos/config',
-  '/pos/reports',
   '/pos/static/css/tokens.css',
   '/pos/static/css/common.css',
   '/pos/static/js/app-init.js',
@@ -132,8 +122,8 @@ self.addEventListener('fetch', function (event) {
     return;
   }
 
-  // Don't cache login page
-  if (url.pathname === '/pos/login' || url.pathname === '/pos/login/') {
+  // HTML pages -> network-first (always fresh)
+  if (req.headers.get('accept') && req.headers.get('accept').indexOf('text/html') !== -1) {
     event.respondWith(networkFirst(req));
     return;
   }
@@ -181,7 +171,7 @@ self.addEventListener('fetch', function (event) {
     return;
   }
 
-  // Everything else -> cache-first
+  // Everything else (JS, CSS, images) -> cache-first
   event.respondWith(cacheFirst(req));
 });