cmd/tsconnect: prefetch main.wasm when serving

Avoids waterfalling of requests from the file (its load is triggered
from JavaScript).

Also has other cleanups to index.html, adding a <title> and moving the
<script> to being loaded sooner (but still not delaying page rendering
by using the defer attribute).

Fixes #5141
Fixes #5135

Signed-off-by: Mihai Parparita <mihai@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f