feat: Add copy link to tag support

[alnoki]

Add Tag Support for Permalinks

Summary

This PR adds support for creating permalinks to Git tags, alongside the existing branch, commit, and default branch options. Tags provide a more readable alternative to commit hashes for versioned releases.

Changes

New Features

• "Copy Link to Selection (at current tag)" command - directly copy a link using the current tag (if HEAD is at a tag)
• "Current tag" preset option in the "choose type" quick pick dialog
• "Tags" section in the quick pick showing all repository tags
• tag option for the gitweblinks.linkType setting to use tags by default

Files Modified

• src/types.ts - Added 'tag' to LinkType and LinkTargetRef.type unions
• src/constants.ts - Added copySelectionToTag command constant
• src/settings.ts - Handle 'tag' in getDefaultLinkType()
• src/link-handler.ts - Added 'tag' case in getRef() using git describe --exact-match --tags HEAD
• src/commands/get-link-command.ts - Added "Current tag" preset and "Tags" section in quick pick
• src/commands/index.ts - Registered copySelectionToTag command
• package.json - Added command definition and 'tag' to linkType enum

Test Updates

The quick pick item indices in get-link-command.test.ts were updated to account for the new structure:

Previous structure (10 items):

• 3 presets → "Branches" separator → 3 branches → "Commits" separator → 3 commits

New structure (12 items):

• 4 presets (added "Current tag") → "Branches" separator → 3 branches → "Tags" separator → "Commits" separator → 3 commits

This shifted the branch item indices by 1 (from [4,5,6] to [5,6,7]) and commit item indices by 2 (from [8,9,10] to [10,11,12]).

Implementation Details

• Tags are retrieved using git describe --exact-match --tags HEAD for the current tag
• All tags are listed using git tag -l --format='%(refname:short) %(objectname:short) %(objectname)'
• If HEAD is not at a tag, the "Current tag" preset shows an empty description
• Tags use the same URL template as branches (the {{ ref }} placeholder contains the tag name)