feat(web): every sidebar calendar can be hidden (shared, birthday, ical too)

Equal rights for all calendar types: the sidebar remove button is now a uniform
"hide" (eye) for every calendar instead of delete-for-some / nothing-for-shared.

- Owned local (incl. birthday) and iCal now hide via the server sidebar_hidden
  flag (delete stays available in Settings' calendar table).
- Calendars shared with me get a per-device sidebar hide (they can't carry a
  server flag); their events are filtered out while hidden, and the Settings
  calendar table's "shared with me" rows gain an un-hide eye toggle.
- External caldav/google/ha unchanged.

Group calendars intentionally left as-is for now.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v88';
+export const APP_VERSION = 'v89';