fix(android): edge-to-edge insets + show all calendars in the filter

1) Burger menu (and other bottom sheets) had rows hidden behind the system
   navigation bar: MainActivity never called enableEdgeToEdge(), so the sheets'
   navigationBarsPadding resolved to 0. Enable edge-to-edge and place the insets
   ourselves — top bar statusBarsPadding, content/FAB navigationBarsPadding,
   auth screens systemBarsPadding — and add navigationBarsPadding (+ imePadding
   for the editor) to the Filter/Groups/Accounts/Editor sheets.

2) The calendar filter only listed calendars that had events in the loaded
   range, so empty calendars couldn't be toggled. Load the full calendar list
   from all sources (loadAllCalendars) and merge it with the event-derived
   entries — matching iOS, which already shows the complete list.

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

app/src/main/java/com/scarriffle/calendarr/MainActivity.kt

@@ -3,6 +3,7 @@ package com.scarriffle.calendarr
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
 import androidx.core.splashscreen.SplashScreen.Companion.installSplashScreen
 import com.scarriffle.calendarr.ui.CalendarrRoot
 import dagger.hilt.android.AndroidEntryPoint
@@ -13,6 +14,10 @@ class MainActivity : ComponentActivity() {
         // Covers the window from the first frame (incl. warm-start), then hands
         // off to the in-app branded splash which stays until data is loaded.
         installSplashScreen()
+        // Draw edge-to-edge so system-bar insets reach every window, including
+        // ModalBottomSheets — otherwise navigationBarsPadding() inside the sheets
+        // resolves to 0 and the bottom menu rows hide behind the nav bar.
+        enableEdgeToEdge()
         super.onCreate(savedInstanceState)
         setContent {
             CalendarrRoot()