Add OpenAPI docs, frontend, migrations, and API updates

- OpenAPI: add missing endpoints (add-from-url, subscriptions, public availability)
- OpenAPI: CalendarSubscription schema, Subscriptions tag
- Frontend app
- Migrations: count_for_availability, subscriptions_sync, user_preferences, calendar_settings
- Config, rate limit, auth, calendar, booking, ICS, availability, user service updates

Made-with: Cursor

frontend/node_modules/electron-to-chromium/index.js

@@ -0,0 +1,36 @@
+var versions = require('./versions');
+var fullVersions = require('./full-versions');
+var chromiumVersions = require('./chromium-versions');
+var fullChromiumVersions = require('./full-chromium-versions');
+
+var electronToChromium = function (query) {
+  var number = getQueryString(query);
+  return number.split('.').length > 2 ? fullVersions[number] : versions[number] || undefined;
+};
+
+var chromiumToElectron = function (query) {
+  var number = getQueryString(query);
+  return number.split('.').length > 2 ? fullChromiumVersions[number] : chromiumVersions[number] || undefined;
+};
+
+var electronToBrowserList = function (query) {
+  var number = getQueryString(query);
+  return versions[number] ? "Chrome >= " + versions[number] : undefined;
+};
+
+var getQueryString = function (query) {
+  var number = query;
+  if (query === 1) { number = "1.0" }
+  if (typeof query === 'number') { number += ''; }
+  return number;
+};
+
+module.exports = {
+  versions: versions,
+  fullVersions: fullVersions,
+  chromiumVersions: chromiumVersions,
+  fullChromiumVersions: fullChromiumVersions,
+  electronToChromium: electronToChromium,
+  electronToBrowserList: electronToBrowserList,
+  chromiumToElectron: chromiumToElectron
+};