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>

CHANGELOG.md

@@ -5,6 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.11.1] — 2026-06-28
+
+### 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]).
+
 ## [2.11.0] — 2026-06-27
 
 ### Added
@@ -685,3 +694,4 @@ automatically, with zero telemetry and no internet permission.
 [#6]: https://codeberg.org/jlmakiola/calendula/issues/6
 [#7]: https://codeberg.org/jlmakiola/calendula/issues/7
 [#8]: https://codeberg.org/jlmakiola/calendula/issues/8
+[#9]: https://codeberg.org/jlmakiola/calendula/issues/9