feat: optimize file icons, UI, share direct links, and upload performance

- Replace CSS-only file icons with SVG icons for each file type (folder, image, video, audio, archive, document, app)
- Add navigation icons to left sidebar (Baidu Netdisk style)
- Enlarge file cards (108px -> 120px) with smoother transitions
- Add direct links section to share page with copy/delete actions
- Add Rust bridge commands for fetching and deleting direct links
- Optimize local storage put() to use rename-first strategy instead of copyFileSync for instant large file completion
- Show "server processing" status during upload finalization instead of appearing stuck

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/storage.js

@@ -244,16 +244,25 @@ class LocalStorageClient {
     const tempPath = `${destPath}.uploading_${Date.now()}`;
 
     try {
-      // 复制到临时文件
-      fs.copyFileSync(localPath, tempPath);
-
       // 如果目标文件存在，先删除
       if (fs.existsSync(destPath)) {
         fs.unlinkSync(destPath);
       }
 
-      // 重命名临时文件为目标文件
-      fs.renameSync(tempPath, destPath);
+      // 优先尝试 rename（同文件系统下瞬时完成，大文件不再需要逐字节复制）
+      let movedDirectly = false;
+      try {
+        fs.renameSync(localPath, destPath);
+        movedDirectly = true;
+      } catch (renameErr) {
+        if (renameErr.code === 'EXDEV') {
+          // 跨文件系统，回退到 copy + rename
+          fs.copyFileSync(localPath, tempPath);
+          fs.renameSync(tempPath, destPath);
+        } else {
+          throw renameErr;
+        }
+      }
 
       // 更新已使用空间（使用净增量）
       if (netIncrease !== 0) {
@@ -262,7 +271,7 @@ class LocalStorageClient {
     } catch (error) {
       // 清理临时文件
       if (fs.existsSync(tempPath)) {
-        fs.unlinkSync(tempPath);
+        try { fs.unlinkSync(tempPath); } catch (_) {}
       }
       throw error;
     }