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/build.gradle.kts

@@ -54,6 +54,7 @@ android {
 dependencies {
     coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.0.4")
     implementation("androidx.core:core-ktx:1.12.0")
+    implementation("androidx.core:core-splashscreen:1.0.1")
     implementation("com.google.android.material:material:1.11.0")
     implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.7.0")
     implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")