feat: add maximum content width constraint for wide displays (Closes #2)

Add MAX_CONTENT_WIDTH (1200dp) to UiConstants and wrap scaffold content
in a centered Box with widthIn(max) to prevent uncomfortable stretching
on ultra-wide monitors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sharedUI/src/commonMain/kotlin/org/shahondin1624/App.kt

@@ -20,6 +20,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
 import kotlinx.coroutines.launch
 import org.jetbrains.compose.ui.tooling.preview.Preview
+import org.shahondin1624.lib.components.UiConstants
 import org.shahondin1624.lib.components.charactermodel.attributespage.AttributesPage
 import org.shahondin1624.model.EXAMPLE_CHARACTER
 import org.shahondin1624.theme.AppTheme
@@ -121,11 +122,17 @@ private fun AppContent(
                 )
             }
         ) { paddingValues ->
-            Column(
+            Box(
                 modifier = Modifier
                     .fillMaxSize()
                     .padding(paddingValues)
-                    .windowInsetsPadding(WindowInsets.safeDrawing)
+                    .windowInsetsPadding(WindowInsets.safeDrawing),
+                contentAlignment = Alignment.TopCenter
+            ) {
+                Column(
+                    modifier = Modifier
+                        .widthIn(max = UiConstants.MAX_CONTENT_WIDTH)
+                        .fillMaxWidth()
                         .padding(16.dp),
                     horizontalAlignment = Alignment.CenterHorizontally
                 ) {
@@ -134,3 +141,4 @@ private fun AppContent(
             }
         }
     }
+}

sharedUI/src/commonMain/kotlin/org/shahondin1624/lib/components/UiConstants.kt

@@ -4,4 +4,7 @@ import androidx.compose.ui.unit.dp
 
 object UiConstants {
     val SMALL_PADDING = 6.dp
+
+    /** Maximum width for the main content area to prevent uncomfortable stretching on ultra-wide displays. */
+    val MAX_CONTENT_WIDTH = 1200.dp
 }