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]

tests/scene_generator_test.rs

@@ -38,6 +38,7 @@ fn generator_writes_registration_ready_package_with_scene_toml() {
         scene_id: "sample-report-scene".to_string(),
         scene_name: "示例报表场景".to_string(),
         scene_kind: None,
+        target_url: None,
         output_root: output_root.clone(),
         lessons_path: PathBuf::from("docs/superpowers/references/tq-lineloss-lessons-learned.toml"),
     })
@@ -152,6 +153,7 @@ fn generator_emits_monitoring_template() {
         scene_id: "sample-monitor-scene".to_string(),
         scene_name: "示例监测场景".to_string(),
         scene_kind: Some(SceneKind::Monitoring),
+        target_url: None,
         output_root: output_root.clone(),
         lessons_path: PathBuf::from("docs/superpowers/references/tq-lineloss-lessons-learned.toml"),
     })