Added warning message about git extension no longer being enabled by default

[aaronrsun]

Addresses: #2165
Spec doc: #2196

[Copilot]

Pull request overview

Adds a post-init warning to inform users that the bundled git extension will no longer be enabled by default starting in v1.0.0, and introduces tests/spec documentation for that notice.

Changes:

• Track whether the bundled git extension was freshly installed during specify init and, if so, print a Rich warning panel about the upcoming default-behavior change.
• Add CLI tests covering when the deprecation notice should/shouldn’t appear.
• Add a feature spec documenting the motivation and acceptance criteria.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/specify_cli/__init__.py	Tracks fresh git extension installation and prints an “Upcoming Change” warning panel after init completes.
tests/extensions/git/test_git_extension.py	Adds coverage to ensure the warning appears only when the git extension is newly installed (and not with --no-git).
.specify/features/git-extension-deprecation-notice/spec.md	Documents the intended behavior and messaging for the deprecation notice.

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[Copilot]

Pull request overview

Adds a user-facing warning during specify init to notify users that the bundled git extension will stop being enabled by default starting in v1.0.0, along with tests to validate when the notice appears.

Changes:

• Track whether the bundled git extension was freshly installed during specify init.
• Print a yellow Rich Panel notice after initialization when the git extension was auto-installed.
• Add CLI-level tests covering notice shown/not shown scenarios.

Show a summary per file

File	Description
src/specify_cli/__init__.py	Tracks fresh git extension install and prints a post-init deprecation notice panel.
tests/extensions/git/test_git_extension.py	Adds tests asserting the notice appears only on fresh git extension install and not with --no-git / already-installed scenarios.

Copilot's findings

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• Files reviewed: 2/2 changed files
• Comments generated: 1

[mnriem]

Would it be possible that the extension itself vends the message during its setup?