Add dev favicons and conditional favicon logic

Introduces development favicons for ChatUI and HuggingChat, and updates layout to use these when PUBLIC_ORIGIN is not set. This helps distinguish development environments from production by displaying different favicons.

Author: gary149

src/routes/+layout.svelte

@@ -197,18 +197,22 @@
 		<meta property="og:description" content={publicConfig.PUBLIC_APP_DESCRIPTION} />
 	{/if}
 	<link rel="icon" href="{publicConfig.assetPath}/icon.svg" type="image/svg+xml" />
-	<link
-		rel="icon"
-		href="{publicConfig.assetPath}/favicon.svg"
-		type="image/svg+xml"
-		media="(prefers-color-scheme: light)"
-	/>
-	<link
-		rel="icon"
-		href="{publicConfig.assetPath}/favicon-dark.svg"
-		type="image/svg+xml"
-		media="(prefers-color-scheme: dark)"
-	/>
+	{#if publicConfig.PUBLIC_ORIGIN}
+		<link
+			rel="icon"
+			href="{publicConfig.assetPath}/favicon.svg"
+			type="image/svg+xml"
+			media="(prefers-color-scheme: light)"
+		/>
+		<link
+			rel="icon"
+			href="{publicConfig.assetPath}/favicon-dark.svg"
+			type="image/svg+xml"
+			media="(prefers-color-scheme: dark)"
+		/>
+	{:else}
+		<link rel="icon" href="{publicConfig.assetPath}/favicon-dev.svg" type="image/svg+xml" />
+	{/if}
 	<link rel="apple-touch-icon" href="{publicConfig.assetPath}/apple-touch-icon.png" />
 	<link rel="manifest" href="{publicConfig.assetPath}/manifest.json" />