Externalize git hook logic into a dedicated git-hooks package

[coisa]

Context

Issue #296 was merged as an intermediate fix while the broader git-hooks extraction work is still pending.

resources/git-hooks still contains the hook runtime logic, and the GrumPHP binary fallbacks were fixed directly in this repository in a temporary way.

Problem

We need a dedicated package boundary for Git hooks instead of keeping lifecycle scripts inside dev-tools, so this repository can depend on the extracted hook package and avoid duplicated or environment-specific logic.

Scope

• Create and publish a dedicated fast-forward/git-hooks package/repository (or integrate the final target package that already exists) to host the managed Git hook scripts.
• Migrate existing hook scripts from resources/git-hooks/* while preserving behavior for:
  • commit-msg
  • post-checkout
  • post-merge
  • pre-commit
• Update dev-tools synchronization and installation flow to consume the externalized package instead of embedding the full hook logic.
• Keep local and global execution compatibility, including GrumPHP resolution order and project-local overrides.
• Keep documentation and generated output in sync with the new source-of-truth for hooks.

Acceptance Criteria

• Hook execution logic is implemented in the dedicated git-hooks package and no longer maintained only inside resources/git-hooks.
• dev-tools git-hooks installs and updates the expected hooks in consumer repositories.
• GrumPHP invocation order remains unchanged in behavior for managed workflows:
  1. vendor/bin/grumphp
  2. vendor/bin/grumphp.phar
  3. grumphp in PATH
• Existing and regression tests for GitHooksCommand and self-update/global path checks remain green.
• README/usage and command help that mention Git hook installation reflect the new package flow.
• Any required changelog note is added for user-facing or release-process behavior changes.

Notes

• This issue should be treated as the follow-up architecture step after Extract Git hook logic into fast-forward/git-hooks package #296.
• Related: Use resilient GrumPHP binary resolution in packaged git hooks #331 (GrumPHP fallback in hooks) and Fix global GrumPHP hook fallback using an invalid packaged config path #305 (path fallback behavior).