feat: module toggles in POS config and Instance Manager

- Add GET/PUT /pos/api/config/modules endpoints in POS config_bp.py
- Update sidebar.js to filter nav items based on enabled modules
- Add Modules section to POS config.html with toggles for WhatsApp, Marketplace, MercadoLibre
- Add module load/save logic to POS config.js
- Preload modules in app-init.js for sidebar caching

- Add tenant module management to Instance Manager
  - get_tenant_modules / update_tenant_modules in tenant_service.py
  - GET/PUT /api/tenants/<id>/modules endpoints in tenants_bp.py
  - Add modules modal to manager index.html
  - Add module editing UI and logic to manager.js
  - Add toggle-switch CSS to manager.css

pos/static/pwa/sw.js

@@ -179,7 +179,7 @@ function cacheFirst(request) {
   return caches.match(request).then(function (cached) {
     if (cached) {
       fetch(request).then(function (response) {
-        if (response && response.status === 200) {
+        if (response && response.status === 200 && request.method === 'GET') {
           caches.open(CACHE_NAME).then(function (cache) {
             cache.put(request, response);
           });
@@ -188,7 +188,7 @@ function cacheFirst(request) {
       return cached;
     }
     return fetch(request).then(function (response) {
-      if (response && response.status === 200) {
+      if (response && response.status === 200 && request.method === 'GET') {
         var clone = response.clone();
         caches.open(CACHE_NAME).then(function (cache) {
           cache.put(request, clone);
@@ -201,7 +201,7 @@ function cacheFirst(request) {
 
 function networkFirst(request) {
   return fetch(request).then(function (response) {
-    if (response && response.status === 200) {
+    if (response && response.status === 200 && request.method === 'GET') {
       var clone = response.clone();
       caches.open(CACHE_NAME).then(function (cache) {
         cache.put(request, clone);