fix(intents): register calendar intent filters so Calendula can be the default calendar (#9)

Calendula didn't declare the intent filters launchers and the system use for
calendar actions, so it never appeared in the "default calendar app" chooser —
on every platform, not just GrapheneOS (issue #9). Android exposes no API for an
app to set itself default, so registering these filters is the only way users can
pick it from the system picker.

Adds to MainActivity:
- MAIN + APP_CALENDAR — the "open the calendar app" action the OS/launchers use.
- VIEW on content://com.android.calendar/time/<epochMillis> and the time/epoch
  mime type — a launcher/clock date tap. The provider's time Uri is parsed into a
  LocalDate and opened on the day view, rooted over the default home view (a new
  sourceless WidgetNavRequest.OpenDate). The .ics import path now ignores the
  calendar provider host so a date tap isn't mistaken for a file to import.

Bumps to 2.11.1.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fastlane/metadata/android/en-US/changelogs/21101.txt

@@ -0,0 +1,6 @@
+### Fixed
+- Calendula can now be set as your default calendar app. It registers the
+  calendar-app intent filters the system uses, so it appears in the chooser when
+  you tap a date in a launcher or clock — and opening one takes you straight to
+  that day. Android has no way for an app to make itself the default, so you pick
+  it once from the system picker. Thanks to @abrossimow for the report ([#9]).