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/caniuse-lite/dist/unpacker/region.js

@@ -0,0 +1,22 @@
+'use strict'
+
+const browsers = require('./browsers').browsers
+
+function unpackRegion(packed) {
+  return Object.keys(packed).reduce((list, browser) => {
+    let data = packed[browser]
+    list[browsers[browser]] = Object.keys(data).reduce((memo, key) => {
+      let stats = data[key]
+      if (key === '_') {
+        stats.split(' ').forEach(version => (memo[version] = null))
+      } else {
+        memo[key] = stats
+      }
+      return memo
+    }, {})
+    return list
+  }, {})
+}
+
+module.exports = unpackRegion
+module.exports.default = unpackRegion