fix(demo): cache-bust vocab JS + defensive fallback when loadFromFlatFreq missing

Yesterday's switch to the APK dict required a new
SwipeVocabulary.loadFromFlatFreq method. Fastly/Cloudflare and the
browser both cache swipe-vocabulary.js for 4 h (max-age=14400), so
users who had /demo/ open — or who hit the edge cache before it
invalidated — got a stale JS without the new method, producing
"swipeVocabulary.loadFromFlatFreq is not a function" on load.

Two defenses:
- Version-query the demo's three support scripts (swipe-vocabulary,
  custom-dictionary, niche-words-loader). Future JS changes bump
  the `?v=` token, forcing both the CDN and the browser to fetch
  fresh.
- In loadVocabulary(), typeof-check the method before calling it;
  if an ancient cached version is somehow still loaded, silently
  fall back to loadFromJSON (the 150k vocab) instead of hard-failing.

— opus 4.7

Author: tribixbite

web_demo/demo/index.html

@@ -8,11 +8,13 @@
     <!-- ONNX Runtime Web -->
     <script src="https://cdn.jsdelivr.net/npm/onnxruntime-web@1.18.0/dist/ort.min.js"></script>
     <!-- Swipe Vocabulary Module -->
-    <script src="swipe-vocabulary.js"></script>
+    <!-- ?v=<hash> cache-busts Cloudflare/Fastly edge + browser cache so users
+         don't get stranded on an old JS that predates loadFromFlatFreq et al. -->
+    <script src="swipe-vocabulary.js?v=20260419b"></script>
     <!-- Custom Dictionary Support -->
-    <script src="custom-dictionary.js"></script>
+    <script src="custom-dictionary.js?v=20260419b"></script>
     <!-- Niche Words Loader -->
-    <script src="niche-words-loader.js"></script>
+    <script src="niche-words-loader.js?v=20260419b"></script>
     <script>
         tailwind.config = {
             theme: {
@@ -730,7 +732,15 @@ <h3 class="text-lg font-semibold text-white mb-3">Dictionary Statistics</h3>
                 swipeVocabulary = new SwipeVocabulary();
                 let loaded = false;
 
-                if (DEMO_CONFIG.dictionary === 'apk') {
+                // Defensive: an old cached swipe-vocabulary.js may predate
+                // loadFromFlatFreq. If the method is missing, skip straight
+                // to the 150k JSON loader instead of hard-failing.
+                const canLoadFlat = typeof swipeVocabulary.loadFromFlatFreq === 'function';
+                if (!canLoadFlat) {
+                    console.warn('swipe-vocabulary.js is stale (no loadFromFlatFreq); falling back to full 150k vocab');
+                }
+
+                if (DEMO_CONFIG.dictionary === 'apk' && canLoadFlat) {
                     updateLoadingStatus('Loading APK dictionary (52k, ~930KB)...');
                     loaded = await swipeVocabulary.loadFromFlatFreq('en_enhanced.json');
                     if (!loaded) {