feat: multi-day event bars, readiness-gated splash, top-bar spinner, 2-line titles, detail animation

- Month view now draws multi-day events as continuous bars (lane packing,
  per-week column span clipped at week boundaries, +N overflow) instead of a
  chip on every day; events bucketed per week once + memoized packing for
  smooth scrolling
- Startup: core-splashscreen covers the window from frame 0 (no warm-start
  flash); the in-app splash stays until the first events finish loading (loading
  starts behind the splash via an early-obtained CalendarViewModel + ready flow),
  so you no longer enter a laggy app
- Background load shows a small spinner in the top bar (removed the linear bar)
- Week/Day titles wrap to two smaller lines (no more truncation)
- Event detail opens with a slide+fade animation

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/res/values/themes.xml

@@ -8,4 +8,11 @@
         <item name="android:navigationBarColor">@android:color/black</item>
         <item name="android:windowLightStatusBar">false</item>
     </style>
+
+    <!-- System splash (core-splashscreen); covers the window from frame 0. -->
+    <style name="Theme.Calendarr.Starting" parent="Theme.SplashScreen">
+        <item name="windowSplashScreenBackground">@android:color/black</item>
+        <item name="windowSplashScreenAnimatedIcon">@drawable/splash_icon</item>
+        <item name="postSplashScreenTheme">@style/Theme.Calendarr</item>
+    </style>
 </resources>