release: cut v2.3.0 — Material 3 grouped-list redesign of Settings, calendars & drawer

One shared Material 3 grouped-list blueprint, modelled on the ReFra gallery app
and extracted to ui/common/GroupedList.kt: CollapsingScaffold (a LargeTopAppBar
whose large title collapses into the bar on scroll) and GroupedRow
(Position-based corner grouping so a run of rows reads as one rounded card, with
press-animated corners and selected/minHeight knobs).

Settings: restructured into a category hub (About card on top, version mark at
the foot) with sliding sub-pages for Appearance, the new-event form and
Notifications. Theme, week-start and language pickers migrated from DropdownMenu
to OptionCard dialogs; token-based icon chips. New ic_gitea.xml (Simple Icons,
verbatim path) for the About "Source" button; en+de strings.

Calendar manager: same collapsing scaffold + grouped rows; shared
CalendarColorChip (neutral chip with a pastelised calendar glyph) replaces the
bright colour swatch.

Navigation drawer: branded header, grouped View switcher (active view
highlighted via secondaryContainer), filter list restyled to grouped rows with a
trailing checkbox; the whole drawer now scrolls as one.

Cards use surfaceContainerHigh for readable contrast against surface. Version
bumped to 2.3.0 / 20300. UI-only; unit tests green.

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

app/build.gradle.kts

@@ -28,8 +28,8 @@ android {
         // the tag, with versionCode = MAJOR*10000 + MINOR*100 + PATCH
         // (e.g. v2.0.0 -> 20000). These committed values are the dev/local
         // default; keep them matching the latest released tag. See docs/RELEASING.md.
-        versionCode = 20200
-        versionName = "2.2.0"
+        versionCode = 20300
+        versionName = "2.3.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }