feat(web): add resource preloading for fonts and markdown files

- Add <link rel="preload"> tags in HTML for browser-level caching of all fonts and markdown resources
- Implement preloadFont() API in Kotlin to prevent FOUT during app startup
- Preload markdown files via produceState() to warm Compose resource cache
- Manrope fonts (macosui) preload via separate webMain composable to respect internal visibility
- Only render App() after all resources (fonts + markdown) are ready

Implements Method 1 (HTML preload) and Method 2 (Compose Multiplatform API) from Kotlin docs:
https://kotlinlang.org/docs/multiplatform/compose-web-resources.html#preloading-of-resources-for-web-targets

Author: kdroidFilter

macosui/src/webMain/kotlin/io/github/kdroidfilter/nucleus/ui/apple/macos/theme/PreloadResources.web.kt

@@ -0,0 +1,21 @@
+package io.github.kdroidfilter.nucleus.ui.apple.macos.theme
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import composemacosui.macosui.generated.resources.Res
+import composemacosui.macosui.generated.resources.manrope_bold
+import composemacosui.macosui.generated.resources.manrope_medium
+import composemacosui.macosui.generated.resources.manrope_regular
+import composemacosui.macosui.generated.resources.manrope_semibold
+import org.jetbrains.compose.resources.ExperimentalResourceApi
+import org.jetbrains.compose.resources.preloadFont
+
+@OptIn(ExperimentalResourceApi::class)
+@Composable
+fun preloadMacosResources(): Boolean {
+    val regular by preloadFont(Res.font.manrope_regular)
+    val medium by preloadFont(Res.font.manrope_medium)
+    val semibold by preloadFont(Res.font.manrope_semibold)
+    val bold by preloadFont(Res.font.manrope_bold)
+    return regular != null && medium != null && semibold != null && bold != null
+}

sample/src/webMain/kotlin/io/github/kdroidfilter/nucleus/ui/apple/macos/sample/main.kt

@@ -1,9 +1,36 @@
 package io.github.kdroidfilter.nucleus.ui.apple.macos.sample
 
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.produceState
 import androidx.compose.ui.ExperimentalComposeUiApi
 import androidx.compose.ui.window.ComposeViewport
+import composemacosui.sample.generated.resources.jetbrains_mono_bold
+import composemacosui.sample.generated.resources.jetbrains_mono_regular
+import io.github.kdroidfilter.nucleus.ui.apple.macos.theme.preloadMacosResources
+import org.jetbrains.compose.resources.ExperimentalResourceApi
+import org.jetbrains.compose.resources.preloadFont
+import composemacosui.sample.generated.resources.Res as SampleRes
 
-@OptIn(ExperimentalComposeUiApi::class)
+@OptIn(ExperimentalComposeUiApi::class, ExperimentalResourceApi::class)
 fun main() {
-    ComposeViewport { App() }
+    ComposeViewport {
+        val macosReady = preloadMacosResources()
+        val jbMonoRegular by preloadFont(SampleRes.font.jetbrains_mono_regular)
+        val jbMonoBold by preloadFont(SampleRes.font.jetbrains_mono_bold)
+
+        val mdGettingStarted by produceState<ByteArray?>(null) {
+            value = SampleRes.readBytes("files/getting_started.md")
+        }
+        val mdLicense by produceState<ByteArray?>(null) {
+            value = SampleRes.readBytes("files/license.md")
+        }
+
+        val allReady = macosReady &&
+            jbMonoRegular != null && jbMonoBold != null &&
+            mdGettingStarted != null && mdLicense != null
+
+        if (allReady) {
+            App()
+        }
+    }
 }

sample/src/webMain/resources/index.html

@@ -5,6 +5,16 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Compose Mac OS 26 UI</title>
     <link type="text/css" rel="stylesheet" href="styles.css">
+    <!-- Fonts -->
+    <link rel="preload" href="./composeResources/composemacosui.macosui.generated.resources/font/manrope_regular.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.macosui.generated.resources/font/manrope_medium.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.macosui.generated.resources/font/manrope_semibold.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.macosui.generated.resources/font/manrope_bold.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.sample.generated.resources/font/jetbrains_mono_regular.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.sample.generated.resources/font/jetbrains_mono_bold.ttf" as="fetch" type="font/ttf" crossorigin/>
+    <!-- Markdown files -->
+    <link rel="preload" href="./composeResources/composemacosui.sample.generated.resources/files/getting_started.md" as="fetch" crossorigin/>
+    <link rel="preload" href="./composeResources/composemacosui.sample.generated.resources/files/license.md" as="fetch" crossorigin/>
     <style>
         #boot-screen {
             position: fixed;