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/date-fns/parse/_lib/parsers/EraParser.js

@@ -0,0 +1,39 @@
+import { Parser } from "../Parser.js";
+
+export class EraParser extends Parser {
+  priority = 140;
+
+  parse(dateString, token, match) {
+    switch (token) {
+      // AD, BC
+      case "G":
+      case "GG":
+      case "GGG":
+        return (
+          match.era(dateString, { width: "abbreviated" }) ||
+          match.era(dateString, { width: "narrow" })
+        );
+
+      // A, B
+      case "GGGGG":
+        return match.era(dateString, { width: "narrow" });
+      // Anno Domini, Before Christ
+      case "GGGG":
+      default:
+        return (
+          match.era(dateString, { width: "wide" }) ||
+          match.era(dateString, { width: "abbreviated" }) ||
+          match.era(dateString, { width: "narrow" })
+        );
+    }
+  }
+
+  set(date, flags, value) {
+    flags.era = value;
+    date.setFullYear(value, 0, 1);
+    date.setHours(0, 0, 0, 0);
+    return date;
+  }
+
+  incompatibleTokens = ["R", "u", "t", "T"];
+}