mvmOS 0.30.0-beta: Browser extensions and more reliable SSH access

This update adds a Browser Extension Builder for public mvmOS apps. An app can now offer a footer button that generates a browser extension preconfigured for the current server, while still allowing its server address to be changed later in the extension settings. It creates a foundation for focused browser tools such as one-click TOTP autofill. SSH Access schedules now update reliably every minute, so multiple keys can follow their own days and hours without interfering with each other.