Request persistent storage after first save

IndexedDB data can be evicted under storage pressure, especially on iOS
Safari. navigator.storage.persist() asks the browser to keep our data. On
Chromium+Firefox it succeeds silently when conditions allow (installed PWA,
engagement heuristics); on Safari it typically grants only for installed
PWAs.

- persistentStorage.js: isPersisted() and requestPersistence() with graceful
  fallback when the Storage API is unavailable.
- persistence.js: request persistence once, after the first successful save —
  a heuristic that works across Firefox (user gesture context) and
  Chromium/Safari (data-stored context).
- sw.js: bump cache version, precache new file.
- index.html: load new script.

public/index.html

@@ -303,6 +303,7 @@
 <script src="../src/Infrastructure/utils.js"></script>
 <script src="../src/Infrastructure/geolocation.js"></script>
 <script src="../src/Infrastructure/db.js"></script>
+<script src="../src/Infrastructure/persistentStorage.js"></script>
 <script src="../src/Infrastructure/seedOrders.js"></script>
 <script src="../src/Infrastructure/csvLoader.js"></script>
 <script src="../src/Application/state.js"></script>

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE_VERSION = 'duimstok-v1';
+const CACHE_VERSION = 'duimstok-v2';
 
 const APP_SHELL = [
   './',
@@ -19,6 +19,7 @@ const APP_SHELL = [
   '../src/Infrastructure/utils.js',
   '../src/Infrastructure/geolocation.js',
   '../src/Infrastructure/db.js',
+  '../src/Infrastructure/persistentStorage.js',
   '../src/Infrastructure/seedOrders.js',
   '../src/Infrastructure/csvLoader.js',
   '../src/Application/state.js',

src/Application/persistence.js

@@ -1,4 +1,6 @@
 (function (A, I) {
+  let persistenceRequested = false;
+
   function readFormFields() {
     const fd = A.state.formData;
     fd.inspecteur = document.getElementById('inp_inspecteur').value;
@@ -14,6 +16,10 @@
     await I.saveInspection(A.state.formData);
     document.getElementById('statusSaved').textContent =
       'Opgeslagen: ' + new Date().toLocaleTimeString('nl-NL');
+    if (!persistenceRequested) {
+      persistenceRequested = true;
+      I.requestPersistence();
+    }
   };
 
   A.autoSave = function () {

src/Infrastructure/persistentStorage.js

@@ -0,0 +1,20 @@
+(function (I) {
+  function supported() {
+    return navigator.storage && typeof navigator.storage.persist === 'function';
+  }
+
+  I.isPersisted = async function () {
+    if (!supported()) return false;
+    return navigator.storage.persisted();
+  };
+
+  I.requestPersistence = async function () {
+    if (!supported()) return false;
+    if (await navigator.storage.persisted()) return true;
+    try {
+      return await navigator.storage.persist();
+    } catch {
+      return false;
+    }
+  };
+})(window.App.Infrastructure);