feat: add remote_repo variable

[canac]

Add a remote_repo variable that returns the repo name from the remote URL. Unlike repo, it stays consistent even if the clone was renamed.

Feel free to reject, or suggest other names for the variable. But this change would improve my workflow. I hope you don't mind my submitting a PR before opening an issue. Thanks for an amazing developer tool!

AI Disclosure 🤖: I used Claude Code to generate the changes, but reviewed every line and made adjustments.

[worktrunk-bot]

Both sites that populate owner — build_hook_context and UserConfig::format_path — are updated, so the changelog's "available everywhere owner is" holds; GitRemoteUrl::repo() already strips .git in split_namespace_repo, and REPO_VARS, the help table, and the generated doc mirrors all move together.

On the name you asked about: remote_repo reads well beside the existing remote and remote_url, and the prefix is what disambiguates it from repo (the directory on disk), so I'd keep it. Worth an explicit call from @max-sixty before it ships, though — template variable names are part of the config surface, so renaming after a release is a break.