Refactor kantine.js into modular ES6 structure

Moved `kantine.js` into a `src/` directory with multiple modularized files:
- `api.js`: All API calls and constants
- `state.js`: State management (auth, cache, theme, tags, etc.)
- `utils.js`: Helpers for UI and Date formatting
- `ui.js`: DOM manipulation logic
- `events.js`: Initial DOM event listeners and logic hooks
- `actions.js`: Data fetching actions, local processing logic
- `ui_helpers.js`: UI helper functions (rendering modals, handling DOM injections)

Updated the `build-bookmarklet.sh` to compile with Webpack via newly created `webpack.config.js`. Updated all relevant test scripts to use the new output `dist/kantine.bundle.js` and modified logic to work within Webpack scopes.

Co-authored-by: TauNeutrino <1600410+TauNeutrino@users.noreply.github.com>

src/index.js

@@ -0,0 +1,38 @@
+import { injectUI } from './ui.js';
+import { bindEvents } from './events.js';
+import { updateAuthUI, cleanupExpiredFlags, loadMenuCache, isCacheFresh, loadMenuDataFromAPI, startPolling } from './actions.js';
+import { checkForUpdates } from './ui_helpers.js';
+import { authToken } from './state.js';
+
+if (window.__KANTINE_LOADED) {
+    console.log("Kantine Wrapper already loaded.");
+} else {
+    window.__KANTINE_LOADED = true;
+
+    injectUI();
+    bindEvents();
+    updateAuthUI();
+    cleanupExpiredFlags();
+
+    const hadCache = loadMenuCache();
+    if (hadCache) {
+        document.getElementById('loading').classList.add('hidden');
+        if (!isCacheFresh()) {
+            console.log('Cache stale or incomplete – refreshing from API');
+            loadMenuDataFromAPI();
+        } else {
+            console.log('Cache fresh & complete – skipping API refresh');
+        }
+    } else {
+        loadMenuDataFromAPI();
+    }
+
+    if (authToken) {
+        startPolling();
+    }
+
+    checkForUpdates();
+    setInterval(checkForUpdates, 60 * 60 * 1000);
+
+    console.log('Kantine Wrapper loaded ✅');
+}