feat: add hierarchical folder browser for library creation

- Extend API /folders endpoint to support browsing subdirectories with path parameter
- Add depth and has_children fields to FolderItem
- Create FolderBrowser component with tree view navigation
- Create FolderPicker component with input, browse button and popup modal
- Add API proxy route for /api/folders
- Update LibraryForm to use new FolderPicker component
- Fix path handling to correctly resolve /libraries/ subdirectories

apps/backoffice/app/api/folders/route.ts

@@ -0,0 +1,39 @@
+import { NextRequest, NextResponse } from "next/server";
+
+export async function GET(request: NextRequest) {
+  const apiBaseUrl = process.env.API_BASE_URL || "http://api:8080";
+  const apiToken = process.env.API_BOOTSTRAP_TOKEN;
+  
+  if (!apiToken) {
+    return NextResponse.json({ error: "API token not configured" }, { status: 500 });
+  }
+  
+  try {
+    const { searchParams } = new URL(request.url);
+    const path = searchParams.get("path");
+    
+    let apiUrl = `${apiBaseUrl}/folders`;
+    if (path) {
+      apiUrl += `?path=${encodeURIComponent(path)}`;
+    }
+    
+    const response = await fetch(apiUrl, {
+      headers: {
+        Authorization: `Bearer ${apiToken}`,
+      },
+    });
+    
+    if (!response.ok) {
+      return NextResponse.json(
+        { error: `API error: ${response.status}` },
+        { status: response.status }
+      );
+    }
+    
+    const data = await response.json();
+    return NextResponse.json(data);
+  } catch (error) {
+    console.error("Proxy error:", error);
+    return NextResponse.json({ error: "Failed to fetch folders" }, { status: 500 });
+  }
+}