refactor: Modularize UI components and utilities

- Extract UI components into separate JS files
- Centralize configuration values in config.js
- Introduce a dedicated logger module
- Improve file tree drag-and-drop and undo functionality
- Refactor modal handling to a single manager
- Add URL routing support for SPA navigation
- Implement view mode for read-only access

static/js/file-upload.js

@@ -0,0 +1,37 @@
+/**
+ * File Upload Module
+ * Handles file upload dialog for uploading files to the file tree
+ */
+
+/**
+ * Show file upload dialog
+ * @param {string} targetPath - The target directory path
+ * @param {Function} onUpload - Callback function to handle file upload
+ */
+function showFileUploadDialog(targetPath, onUpload) {
+    const input = document.createElement('input');
+    input.type = 'file';
+    input.multiple = true;
+
+    input.addEventListener('change', async (e) => {
+        const files = Array.from(e.target.files);
+        if (files.length === 0) return;
+
+        for (const file of files) {
+            try {
+                await onUpload(targetPath, file);
+            } catch (error) {
+                Logger.error('Upload failed:', error);
+                if (window.showNotification) {
+                    window.showNotification(`Failed to upload ${file.name}`, 'error');
+                }
+            }
+        }
+    });
+
+    input.click();
+}
+
+// Make function globally available
+window.showFileUploadDialog = showFileUploadDialog;
+