Add Display size customization page

Consolidates UI sizing into three percentage sliders surfaced through a
new Settings -> Interface -> Display size page: UI scale (50-150%),
Card size (50-150%), Spacing (25-175%). Each persists immediately via
DataStore; the rest of the app reflects them through
LocalInterfaceCustomization and a root-level LocalDensity override in
MainContent.

The page mirrors HomeSettingsPage's two-column shell: a fixed-width
settings panel on the left, HomePageContent rendering live preview rows
on the right. The page snapshots its own density on entry so the slider
rail stays fixed while UI scale changes the rest of the app.

Includes a one-shot AppUpgradeHandler migration block for installs at or
before 0.6.4-31-g0 that resets the three new percent fields to their
defaults.

app/src/main/java/com/github/damontecres/wholphin/MainContent.kt

@@ -18,6 +18,8 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.RectangleShape
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Density
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.compose.LifecycleEventEffect
@@ -60,7 +62,19 @@ fun MainContent(
 //                            setupNavigationManager.backStack = backStack
         val interfaceCustomization =
             remember(appPreferences) { InterfaceCustomization(appPreferences) }
-        CompositionLocalProvider(LocalInterfaceCustomization provides interfaceCustomization) {
+        val baseDensity = LocalDensity.current
+        val scaledDensity =
+            remember(baseDensity, interfaceCustomization.uiScalePercent) {
+                val factor = interfaceCustomization.uiScalePercent / 100f
+                Density(
+                    density = baseDensity.density * factor,
+                    fontScale = baseDensity.fontScale * factor,
+                )
+            }
+        CompositionLocalProvider(
+            LocalInterfaceCustomization provides interfaceCustomization,
+            LocalDensity provides scaledDensity,
+        ) {
             NavDisplay(
                 backStack = backStack,
                 onBack = { backStack.removeLastOrNull() },