Upload Directories via Web

This implements the option to choose directories when uploading files via the Web UI (The most important part of #52).

When you choose a directory, its file and sub-directory structure will be maintained.

Tested with the latest Safari, Firefox, and Chrome.

Additionally, the Deno version was updated, which required some accessibility improvements as well.

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: denoland/setup-deno@v1
+      - uses: denoland/setup-deno@v2
         with:
           deno-version-file: .dvmrc
       - run: |