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/sw.js

@@ -7,7 +7,7 @@
 // the entry HTML / version files). New releases take effect on the next
 // reload, no manual SW unregister required.
 
-const CACHE_VERSION  = 'calendarr-v35';
+const CACHE_VERSION  = 'calendarr-v36';
 const OFFLINE_SHELL  = ['/', '/index.html'];
 
 self.addEventListener('install', event => {