Support subdirectory deployment and fix API path handling (#311)

* feat: support subdirectory deployment (NEXT_PUBLIC_BASE_PATH)

* removed unwanted check and fix favicon issue

* Use getAssetUrl for manifest assets to avoid undefined NEXT_PUBLIC_BASE_PATH

* Add validation warning for NEXT_PUBLIC_BASE_PATH format

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

lib/base-path.ts

@@ -0,0 +1,37 @@
+/**
+ * Get the base path for API calls and static assets
+ * This is used for subdirectory deployment support
+ *
+ * Example: If deployed at https://example.com/nextaidrawio, this returns "/nextaidrawio"
+ * For root deployment, this returns ""
+ *
+ * Set NEXT_PUBLIC_BASE_PATH environment variable to your subdirectory path (e.g., /nextaidrawio)
+ */
+export function getBasePath(): string {
+    // Read from environment variable (must start with NEXT_PUBLIC_ to be available on client)
+    const basePath = process.env.NEXT_PUBLIC_BASE_PATH || ""
+    if (basePath && !basePath.startsWith("/")) {
+        console.warn("NEXT_PUBLIC_BASE_PATH should start with /")
+    }
+    return basePath
+}
+
+/**
+ * Get full API endpoint URL
+ * @param endpoint - API endpoint path (e.g., "/api/chat", "/api/config")
+ * @returns Full API path with base path prefix
+ */
+export function getApiEndpoint(endpoint: string): string {
+    const basePath = getBasePath()
+    return `${basePath}${endpoint}`
+}
+
+/**
+ * Get full static asset URL
+ * @param assetPath - Asset path (e.g., "/example.png", "/chain-of-thought.txt")
+ * @returns Full asset path with base path prefix
+ */
+export function getAssetUrl(assetPath: string): string {
+    const basePath = getBasePath()
+    return `${basePath}${assetPath}`
+}