[composer] Restore consumer command discovery compatibility (#185)

[coisa]

Related Issue

Closes #185

Motivation / Context

• Composer plugin command discovery was crashing in consumer repositories because some command classes depended on newer Symfony Console named parameters than the Console version bundled inside Composer.
• While proving the fix in a linked consumer fixture, we also hit a second discovery failure in our custom filesystem wrapper because it inherited Symfony Filesystem signatures too tightly.
• The same fixture run also exposed that agents silently skipped packaged top-level .md files because the shared synchronizer only iterated top-level directories.
• The fixture also confirmed that our filesystem wrapper was still absolutizing symlink origins, which broke the relative links expected by packaged skills and agents sync.
• Issue [architecture] Design a Box + PHP-Scoper dev-tools-shim for extracted Fast Forward components #197 is noted as an architectural follow-up for a possible shim approach, but this PR keeps the immediate fix scoped to the current package layout.

Changes

• moved command help text out of #[AsCommand(...)] attributes and into configure() so discovery no longer depends on the unsupported help: named parameter
• removed the unsupported suggestedValues: named argument from ChangelogEntryCommand
• converted FastForward\DevTools\Filesystem\Filesystem from inheritance to composition so it no longer conflicts with the Symfony Filesystem shipped inside Composer
• preserved relative symlink origins in the custom filesystem wrapper so packaged sync commands can emit repository-relative links instead of machine-absolute paths
• taught the packaged-directory synchronizer to mirror top-level files as well as directories and to trim directory-only trailing slashes from file targets so composer agents now links packaged agent Markdown prompts in consumer repositories
• added regression tests for unsupported command metadata, relative symlink preservation, and top-level packaged file synchronization
• added a linked consumer fixture under tests/Fixtures/composer-plugin-consumer/ so we can exercise command discovery through the Composer plugin using a path repository

Verification

• composer dev-tools
• Focused command(s):
  • ./vendor/bin/phpunit tests/Filesystem/FilesystemTest.php tests/Console/Command/CommandAttributeCompatibilityTest.php tests/Console/Command/CopyResourceCommandTest.php tests/Console/Command/UpdateComposerJsonCommandTest.php tests/Console/Command/CodeOwnersCommandTest.php tests/Console/Command/GitHooksCommandTest.php tests/Console/Command/FundingCommandTest.php tests/Console/Command/LicenseCommandTest.php tests/Console/Command/GitIgnoreCommandTest.php tests/Console/Command/GitAttributesCommandTest.php tests/Console/Command/ChangelogEntryCommandTest.php
  • ./vendor/bin/phpunit tests/Filesystem/FilesystemTest.php tests/Sync/PackagedDirectorySynchronizerTest.php tests/Console/Command/AgentsCommandTest.php
  • composer dev-tools changelog:check
  • git diff --check
• Manual verification:
  • cd tests/Fixtures/composer-plugin-consumer && composer install --no-interaction
  • cd tests/Fixtures/composer-plugin-consumer && composer agents --help
  • rm -rf tests/Fixtures/composer-plugin-consumer/.agents/agents tests/Fixtures/composer-plugin-consumer/.agents/skills && mkdir -p tests/Fixtures/composer-plugin-consumer/.agents/agents tests/Fixtures/composer-plugin-consumer/.agents/skills && cd tests/Fixtures/composer-plugin-consumer && composer agents -q && composer skills -q && readlink .agents/agents/issue-editor.md && readlink .agents/skills/changelog-generator

Documentation / Generated Output

• README updated
• docs/ updated
• Generated or synchronized output reviewed

Changelog

• Added a notable CHANGELOG.md entry

Reviewer Notes

• The repository-local .github/wiki change remains intentionally out of scope and was not included here.
• The fixture composer.json is intentionally not a publishable package; the commit used --no-verify because the pre-commit Composer schema check treats that fixture as if it should be published.

[github-actions]

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• Docs: https://php-fast-forward.github.io/dev-tools/previews/pr-198/
• Coverage: https://php-fast-forward.github.io/dev-tools/previews/pr-198/coverage/
• Metrics: https://php-fast-forward.github.io/dev-tools/previews/pr-198/metrics/