feat: add responsive spacing and padding system (Closes #3)

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

@@ -122,6 +122,9 @@ private fun AppContent(
                 )
             }
         ) { paddingValues ->
+            val windowSizeClass = LocalWindowSizeClass.current
+            val contentPadding = UiConstants.Spacing.large(windowSizeClass)
+
             Box(
                 modifier = Modifier
                     .fillMaxSize()
@@ -133,7 +136,7 @@ private fun AppContent(
                     modifier = Modifier
                         .widthIn(max = UiConstants.MAX_CONTENT_WIDTH)
                         .fillMaxWidth()
-                        .padding(16.dp),
+                        .padding(contentPadding),
                     horizontalAlignment = Alignment.CenterHorizontally
                 ) {
                     AttributesPage(character)

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

@@ -1,10 +1,46 @@
 package org.shahondin1624.lib.components
 
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
+import org.shahondin1624.theme.LocalWindowSizeClass
+import org.shahondin1624.theme.WindowSizeClass
 
 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
+
+    /**
+     * Responsive spacing tokens that scale with [WindowSizeClass].
+     *
+     * | Token   | Compact | Medium | Expanded |
+     * |---------|---------|--------|----------|
+     * | small   | 8 dp    | 12 dp  | 16 dp    |
+     * | medium  | 12 dp   | 16 dp  | 20 dp    |
+     * | large   | 12 dp   | 16 dp  | 24 dp    |
+     */
+    object Spacing {
+        /** Small spacing/gap (grid spacing, minor gaps). */
+        fun small(sizeClass: WindowSizeClass): Dp = when (sizeClass) {
+            WindowSizeClass.Compact -> 8.dp
+            WindowSizeClass.Medium -> 12.dp
+            WindowSizeClass.Expanded -> 16.dp
+        }
+
+        /** Medium spacing (content padding, section gaps). */
+        fun medium(sizeClass: WindowSizeClass): Dp = when (sizeClass) {
+            WindowSizeClass.Compact -> 12.dp
+            WindowSizeClass.Medium -> 16.dp
+            WindowSizeClass.Expanded -> 20.dp
+        }
+
+        /** Large spacing (outer page padding, major section dividers). */
+        fun large(sizeClass: WindowSizeClass): Dp = when (sizeClass) {
+            WindowSizeClass.Compact -> 12.dp
+            WindowSizeClass.Medium -> 16.dp
+            WindowSizeClass.Expanded -> 24.dp
+        }
+    }
 }

sharedUI/src/commonMain/kotlin/org/shahondin1624/lib/components/charactermodel/attributespage/AttributesPage.kt

@@ -15,19 +15,25 @@ import androidx.compose.material3.HorizontalDivider
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
+import org.shahondin1624.lib.components.UiConstants
 import org.shahondin1624.model.charactermodel.ShadowrunCharacter
+import org.shahondin1624.theme.LocalWindowSizeClass
 
 @Composable
 fun ColumnScope.AttributesPage(character: ShadowrunCharacter) {
     Box(modifier = Modifier.fillMaxWidth().weight(1f)) {
         val gridState = rememberLazyGridState()
+        val windowSizeClass = LocalWindowSizeClass.current
+        val gridSpacing = UiConstants.Spacing.small(windowSizeClass)
+        val gridPadding = UiConstants.Spacing.medium(windowSizeClass)
+        val dividerPadding = UiConstants.Spacing.medium(windowSizeClass)
 
         LazyVerticalGrid(
             columns = GridCells.Adaptive(minSize = 75.dp),
             state = gridState,
-            modifier = Modifier.fillMaxSize().padding(16.dp),
+            modifier = Modifier.fillMaxSize().padding(gridPadding),
-            horizontalArrangement = Arrangement.spacedBy(8.dp),
+            horizontalArrangement = Arrangement.spacedBy(gridSpacing),
-            verticalArrangement = Arrangement.spacedBy(8.dp)
+            verticalArrangement = Arrangement.spacedBy(gridSpacing)
         ) {
             items(
                 items = character.attributes.getAllAttributes(),
@@ -39,7 +45,7 @@ fun ColumnScope.AttributesPage(character: ShadowrunCharacter) {
 
             item(span = { GridItemSpan(maxLineSpan) }) {
                 HorizontalDivider(
-                    modifier = Modifier.padding(vertical = 16.dp),
+                    modifier = Modifier.padding(vertical = dividerPadding),
                     thickness = 2.dp
                 )
             }

sharedUI/src/commonTest/kotlin/org/shahondin1624/SpacingTest.kt

@@ -0,0 +1,60 @@
+package org.shahondin1624
+
+import androidx.compose.ui.unit.dp
+import org.shahondin1624.lib.components.UiConstants
+import org.shahondin1624.theme.WindowSizeClass
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class SpacingTest {
+
+    @Test
+    fun smallSpacingScalesWithSizeClass() {
+        val compact = UiConstants.Spacing.small(WindowSizeClass.Compact)
+        val medium = UiConstants.Spacing.small(WindowSizeClass.Medium)
+        val expanded = UiConstants.Spacing.small(WindowSizeClass.Expanded)
+
+        assertEquals(8.dp, compact)
+        assertEquals(12.dp, medium)
+        assertEquals(16.dp, expanded)
+        assertTrue(compact < medium, "Compact small should be less than Medium small")
+        assertTrue(medium < expanded, "Medium small should be less than Expanded small")
+    }
+
+    @Test
+    fun mediumSpacingScalesWithSizeClass() {
+        val compact = UiConstants.Spacing.medium(WindowSizeClass.Compact)
+        val medium = UiConstants.Spacing.medium(WindowSizeClass.Medium)
+        val expanded = UiConstants.Spacing.medium(WindowSizeClass.Expanded)
+
+        assertEquals(12.dp, compact)
+        assertEquals(16.dp, medium)
+        assertEquals(20.dp, expanded)
+        assertTrue(compact < medium)
+        assertTrue(medium < expanded)
+    }
+
+    @Test
+    fun largeSpacingScalesWithSizeClass() {
+        val compact = UiConstants.Spacing.large(WindowSizeClass.Compact)
+        val medium = UiConstants.Spacing.large(WindowSizeClass.Medium)
+        val expanded = UiConstants.Spacing.large(WindowSizeClass.Expanded)
+
+        assertEquals(12.dp, compact)
+        assertEquals(16.dp, medium)
+        assertEquals(24.dp, expanded)
+        assertTrue(compact < medium)
+        assertTrue(medium < expanded)
+    }
+
+    @Test
+    fun compactSpacingIsWithinRange() {
+        val small = UiConstants.Spacing.small(WindowSizeClass.Compact)
+        val med = UiConstants.Spacing.medium(WindowSizeClass.Compact)
+        val large = UiConstants.Spacing.large(WindowSizeClass.Compact)
+        assertTrue(small >= 8.dp && small <= 12.dp, "Compact small in 8-12dp range")
+        assertTrue(med >= 8.dp && med <= 12.dp, "Compact medium in 8-12dp range")
+        assertTrue(large >= 8.dp && large <= 12.dp, "Compact large in 8-12dp range")
+    }
+}