Feature/gh32 implement sc tag

[BenjiMilan]

Closes #32

Implement sc tag:

tag check
tag create
tag list
tag push
tag rm
tag show

[Copilot]

Pull request overview

Implements a new sc tag CLI group to manage git tags across either a single git repo or a repo-style multi-project workspace, wiring the CLI into SCBranching and adding the underlying tag command implementations.

Changes:

• Adds sc tag subcommands: list, show, create, rm, push, check.
• Introduces Tag* command implementations to operate on manifest + projects (repo mode) or the current repo (git mode).
• Renames CLI calls from SCBranching.sc_* to SCBranching.* for clean/status/reset.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
src/sc/branching_cli.py	Adds tag command group and subcommands; updates clean/status/reset to new method names.
src/sc/branching/commands/tag.py	New implementations for tag list/show/create/rm/push/check across repo or git project types.
src/sc/branching/branching.py	Wires new tag commands into SCBranching and exposes static methods for CLI use.

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[TB-1993]

I think this looks good. I think we should get a future upgrade ticket for copilots suggestions so we can capture the errors and suggest to users how to fix them. But for now this is good. Ship it!