gitk: visually indicate whether a tag exists on a remote

Hi all,

*Problem*

When browsing history in **gitk**, I often need to know whether a tag I see on a commit was:

  * fetched from a remote (and therefore shared with collaborators), or
  * created only in my local repository and not yet pushed.

For branches this distinction is obvious because gitk lists local and remote-tracking branch heads separately. Tags, however, are shown in a single list, so a locally added tag and one fetched from ­–‐say–‐ `origin` look identical. This can mislead users into thinking a tag is already published when in fact it is not.

*Proposed enhancement*

Add an opt-in visual cue that a tag also exists on at least one remote. Possible UI sketches (open for discussion):

  1. **Suffix** the tag label with the remote name in parentheses, e.g.
     `v1.2.3 (origin)`.
  2. **Colour** or style the tag differently (similar to how remote
     branches are blue vs. local green).
  3. **Tool-tip**: on hover, list the remotes that advertise the tag.

*Why this belongs in gitk*

gitk’s strength is that it gives an at-a-glance view of history. Making tags’ publication state equally transparent would save users a trip to the command line and reduce accidental “forgot to push the tag” issues.

Thanks for considering, and for maintaining gitk!

Best regards, Adi Shavit