v1.13.0 - Saved Launches and Subscribable Calendars

1. Saved Launches - Added browser-based bookmarks, a saved-only filter, live count, and empty state.
2. Full Launch Manifest - Added up to 100 upcoming missions, displayed 24 at a time with a Load More button.
3. Calendar Feed - Added /api/calendar for subscribing to confirmed launches, excluding tentative dates until schedules become more certain.
4. Calendar Setup Page - Added a copyable feed URL, .ics downloads, and subscription instructions.
5. Mission Calendar Files - Added individual calendar events with launch details and links back to mission briefings.
6. API Performance - Added ETags, 304 responses, gzip compression, and stale-cache fallback.
7. Calendar Download Fix - Redirected browser visits to the setup page and fixed download handling.
8. Interface Polish - Improved accessibility, bookmark controls, responsive layouts, and saved-launch indicators.

Published - v1.13.0 is now available on GitHub.