Web: caret/selection fix, reminder options & labels, group mute, rounded modal

- Stop the blinking text caret / selection on non-editable UI chrome
  (headings, buttons, icons, dropdowns): body is user-select:none, with text
  selection opted back in for inputs/textareas. Felt like an editable field.
- Reminder options trimmed to 5/15/30 min, 1 h, 1 day, 1 week (dropped 10 min,
  2 h, 2 days; added 1 week). Labels now read "5 Minuten vorher", "1 Tag
  vorher", "1 Woche vorher" instead of "vor 5 Min." / "vor 1 Tag(en)".
- Group calendars can now be muted (reminder bell) in the sidebar when owned.
- Event modal corners rounded (20px) to match the pill buttons.
- version v45 -> v46.

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 = 'v45';
+export const APP_VERSION = 'v46';