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/docs/release.md

@@ -0,0 +1,19 @@
+# Releasing date-fns
+
+1. First, make sure that the library is built by running `./scripts/build/build.sh` and committing and pushing any change you would have.
+
+2. Then add the changelog entry generated by `npx tsx scripts/release/buildChangelog.ts` to (CHANGELOG.md)[../CHANGELOG.md]. Make sure that the output is valid Markdown and fix if there're any errors. Commit and push the file.
+
+3. Using the version that the changelog script generated, run the command:
+
+   ```bash
+   env VERSION="vX.XX.X" APP_ENV="production" GOOGLE_APPLICATION_CREDENTIALS="secrets/production/key.json" ./scripts/release/release.sh
+   ```
+
+   The script will change `package.json`. **Do not commit the change, and reset it instead**.
+
+4. Now when the package is published, go to [GitHub Releases](https://github.com/date-fns/date-fns/releases) and draft a new version using the changelog entry you generated earlier.
+
+5. Finally, write an announce tweet using the created GitHub release as the tweet link.
+
+You're done, great job!