feat: add folder picker and target_url input to Web UI

- Add /select-folder and /select-file APIs using PowerShell dialogs
- Add --target-url parameter to CLI for explicit target URL override
- Redesign Web UI with folder browse buttons for all path inputs
- Add target_url optional input field for specifying target page URL
- Auto-fill scene-id from selected folder name

🤖 Generated with [Qoder][https://qoder.com]

frontend/scene-generator/generator-runner.js

@@ -2,7 +2,7 @@ const { spawn } = require("child_process");
 const path = require("path");
 
 function runGenerator(params, sseWriter, projectRoot) {
-  const { sourceDir, sceneId, sceneName, sceneKind, outputRoot, lessons } = params;
+  const { sourceDir, sceneId, sceneName, sceneKind, targetUrl, outputRoot, lessons } = params;
 
   const normalize = (p) => p.replace(/\\/g, "/");
 
@@ -24,6 +24,11 @@ function runGenerator(params, sseWriter, projectRoot) {
     args.push("--scene-kind", sceneKind);
   }
 
+  // 如果提供了 targetUrl，添加参数
+  if (targetUrl) {
+    args.push("--target-url", targetUrl);
+  }
+
   args.push(
     "--output-root",
     normalize(outputRoot),