[ BUG ] --debug leaves an HTML dump in TMPDIR for remote documents

[ekalinin]

Describe the bug

With --debug, a run against a remote URL leaves an orphaned ghtoc-remote-txt-*.debug.html file in the temporary directory. Nothing ever removes it, so the files accumulate.

RemoteMd downloads the document into a temporary file and delegates to LocalMd. In debug mode LocalMd writes its HTML dump next to the file it was handed, producing <temp>.debug.html. RemoteMd's deferred cleanup removes only the downloaded copy, not the dump.

The dump is also useless where it lands: it is named after a random temporary file, so there is no obvious way to connect it back to the URL that produced it.

To Reproduce

export TMPDIR=/tmp/ghtoc-dbg && mkdir -p "$TMPDIR"
gh-md-toc --debug https://raw.githubusercontent.com/ekalinin/github-markdown-toc.go/master/README.md > /dev/null
ls -1 "$TMPDIR"

Actual:

ghtoc-remote-txt-482196719.debug.html

Expected: nothing left in TMPDIR, or a dump the user can actually find.

Expected behavior

Two reasonable options, and the choice affects whether --debug stays useful for remote input:

1. Remove it. RemoteMd deletes <temp>.debug.html alongside the temporary Markdown. Smallest change, but --debug then produces nothing inspectable for a remote document, which defeats the flag for that input type.
2. Relocate it. Write the dump into the working directory under a name derived from the URL, for example README.md.debug.html. Keeps the flag useful and matches what already happens for local files, where the dump lands next to the document and is covered by the *.debug.html rule in .gitignore.

Environment (please complete the following information):

• OS: macOS (darwin/arm64), reproduces on any platform
• Version: reproduced at 2.0.1 and on current master

Additional context

Pre-existing, not introduced by any open pull request.

The same class of bug affected --skip-header, where the dump was named after an internal trimmed copy and stranded in TMPDIR the same way. That one is fixed in #79 by naming the dump after the document the user passed rather than after the internal temporary file. RemoteMd was deliberately left out of that change: its display path is a URL, not a filesystem path, so the same fix does not apply directly and the destination is a real decision rather than a mechanical one.

See internal/core/usecase/localmd/localmd.go (debug dump) and internal/core/usecase/remotemd/remotemd.go (temporary file cleanup).