feat(config): support *_MB env vars for upload size limits

- Add `applyMegabytesOrBytesEnv` to accept size settings in either bytes or MB
- Prefer `*_BYTES` when set, otherwise convert `*_MB` to bytes with overflow guard
- Add coverage for MB-based environment overrides
- Introduce `static/js/upload-popups.js` to lazy-load and cache popup templatesfeat(config): support *_MB env vars for upload size limits

- Add `applyMegabytesOrBytesEnv` to accept size settings in either bytes or MB
- Prefer `*_BYTES` when set, otherwise convert `*_MB` to bytes with overflow guard
- Add coverage for MB-based environment overrides
- Introduce `static/js/upload-popups.js` to lazy-load and cache popup templates

static/js/upload-utils.js

@@ -0,0 +1,9 @@
+window.WBUtils = (() => {
+    function renderTemplate(template, data = {}) {
+        return String(template).replace(/\{\{\s*([a-zA-Z0-9_]+)\s*\}\}/g, (_, key) => {
+            return Object.prototype.hasOwnProperty.call(data, key) ? String(data[key]) : "";
+        });
+    }
+
+    return { renderTemplate };
+})();