feat: add pre-push hook commands

[alibro005]

Description

Adds Git pre-push hook support to BeforePush, allowing users to run their branch checks automatically before pushing.

Related Issue

Closes #13

Type of Change

• Bug fix
• New feature
• Tests
• Documentation
• Refactoring
• Other

Changes Made

• Added install-hook and uninstall-hook commands for managing the Git pre-push hook.
• Prevented existing user hooks from being overwritten or removed.
• Made hook installation idempotent and added a marker for BeforePush-managed hooks.
• Added clear handling for Git repository and hook directory errors.
• Added tests for installation, uninstallation, existing hooks, idempotency, and exit-status propagation.

Testing

• uv run pytest -v
• uv run ruff check .
• uv run ruff format --check .
• Tested hook installation and uninstallation manually.
• Tested behavior outside a Git repository.
• Tested hook exit-status propagation.

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