feat: full Compose UI (auth, calendar, events, accounts, settings, profile)

- Root navigation (server setup -> login+2FA -> calendar) with settings-driven theme
- CalendarViewModel mirroring iOS CalendarStore: range-based caching,
  background prefetch, hidden/banished calendar filters, event CRUD
- Five calendar views: Month, Week, Day, Quarter, Agenda (shared time grid)
- Event detail + editor sheets (platform date/time pickers, color override,
  writable-calendar picker) across local/caldav/google/homeassistant
- Calendar filter sheet (per-calendar show/hide)
- Accounts screen: add/delete CalDAV, local, iCal, Home Assistant; list Google
- Settings: view/week-start/language/colors/contrast/hour-height/cache range,
  synced to server
- Profile: email, password change, 2FA enable/disable
- gradlew build (lint + tests + assemble) passes

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

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

@@ -3,14 +3,7 @@ package com.scarriffle.calendarr
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
-import androidx.compose.foundation.layout.Box
-import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Surface
-import androidx.compose.material3.Text
-import androidx.compose.ui.Alignment
-import androidx.compose.ui.Modifier
-import com.scarriffle.calendarr.ui.theme.CalendarrTheme
+import com.scarriffle.calendarr.ui.CalendarrRoot
 import dagger.hilt.android.AndroidEntryPoint
 
 @AndroidEntryPoint
@@ -18,13 +11,7 @@ class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContent {
-            CalendarrTheme {
-                Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
-                    Box(contentAlignment = Alignment.Center, modifier = Modifier.fillMaxSize()) {
-                        Text(text = "Calendarr Android", style = MaterialTheme.typography.headlineMedium)
-                    }
-                }
-            }
+            CalendarrRoot()
         }
     }
 }