Make packaged git hooks the source of truth

[coisa]

Objective

Make resources/git-hooks the source of truth for Fast Forward Git hooks and keep git-hooks responsible for installing those packaged hooks into consumer repositories.

Current Limitation

The git-hooks command still carries GrumPHP initialization behavior, which makes the command do more than install the packaged hook files. That blurs ownership between GrumPHP-generated hooks and the hook templates maintained by this package.

Proposed Work

Refactor Git hook installation so the repository-maintained files in resources/git-hooks are the canonical hook templates. The command should copy those templates to the target hooks directory, apply executable permissions, and preserve the existing overwrite behavior.

Scope

• Add missing packaged hook templates needed by the default hook set, including pre-commit and commit-msg.
• Update packaged post-checkout and post-merge hooks to detect composer.json and composer.lock changes before running dependency refresh.
• Expose useful hook context through DEVTOOLS_* environment variables in post-checkout and post-merge hooks.
• Simplify GitHooksCommand so it only copies packaged hooks and sets executable permissions.
• Update tests and documentation for the new hook installation behavior.

Non-goals

• Changing grumphp.yml configuration or GrumPHP environment variables.
• Updating composer.json metadata generation.
• Replacing GrumPHP as the hook runner.
• Reworking the full sync pipeline beyond the hook source-of-truth change.

Acceptance Criteria

Delivery Criteria

• resources/git-hooks/pre-commit and resources/git-hooks/commit-msg are present as packaged hook templates.
• post-checkout and post-merge run dependency refresh only when composer.json or composer.lock changed.
• GitHooksCommand no longer runs GrumPHP initialization and only copies/chmods packaged hooks.
• Existing source, target, no-overwrite, and executable permission behavior remains deterministic.
• Tests cover the changed command behavior.
• Documentation no longer references the removed --skip-grumphp-init option or GrumPHP initialization step.

Architectural / Isolation Criteria

• MUST: The core logic MUST be isolated into dedicated classes or services instead of living inside command or controller entrypoints.
• MUST: Responsibilities MUST be separated across input resolution, domain logic, processing or transformation, and output rendering when the change is non-trivial.
• MUST: The command or controller layer MUST act only as an orchestrator.
• MUST: The implementation MUST avoid tight coupling between core behavior and CLI or framework-specific I/O.
• MUST: The design MUST allow future extraction or reuse with minimal changes.
• MUST: The solution MUST remain extensible without requiring major refactoring for adjacent use cases.
• MUST: Argument and option resolution MUST be validated separately from command execution logic.
• MUST: Console formatting and rendering MUST stay separate from domain processing.
• MUST: Exit behavior, error messaging, and generated output MUST remain deterministic and testable.