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/ui/CalendarrRoot.kt

@@ -0,0 +1,45 @@
+package com.scarriffle.calendarr.ui
+
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Modifier
+import androidx.hilt.navigation.compose.hiltViewModel
+import com.scarriffle.calendarr.ui.auth.LoginScreen
+import com.scarriffle.calendarr.ui.auth.ServerSetupScreen
+import com.scarriffle.calendarr.ui.calendar.CalendarScreen
+import com.scarriffle.calendarr.ui.theme.CalendarrTheme
+
+@Composable
+fun CalendarrRoot(vm: MainViewModel = hiltViewModel()) {
+    val route by vm.route.collectAsState()
+    val settings by vm.settings.collectAsState()
+
+    CalendarrTheme(settings) {
+        CompositionLocalProvider(
+            LocalLang provides L10n.resolved(settings.language),
+            LocalAppSettings provides settings,
+        ) {
+            Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
+                when (route) {
+                    AppRoute.SETUP -> ServerSetupScreen(onConfigured = vm::onServerConfigured)
+                    AppRoute.LOGIN -> LoginScreen(
+                        serverUrl = vm.serverUrl,
+                        onLoggedIn = vm::onLoggedIn,
+                        onBack = vm::switchServer,
+                    )
+                    AppRoute.MAIN -> CalendarScreen(
+                        onLogout = vm::logout,
+                        onSwitchServer = vm::switchServer,
+                        onSettingsChanged = vm::applyLocalSettings,
+                        onSettingsSynced = vm::refreshSettings,
+                    )
+                }
+            }
+        }
+    }
+}