Refactoring scheduler tabs into multiple pages; adding HTMX PoC

[erewhon]

• Tabs in the scheduler are now separate pages. (Old implementation was Javascript-based, so redirects to a specific tab weren't working, and page reloads would always go back to the first tab.)
• Changed Scheduler toggle to use HTMX and also reflect that you're stopping or starting the scheduler (vs just "toggle")