[feature] Enhance dev-tools:sync to merge and normalize .gitignore entries

[coisa]

Summary

• Added GitIgnore namespace with dedicated classes for .gitignore synchronization:
  • Reader: reads .gitignore entries from both package and project
  • Classifier: classifies entries as directories or files
  • Merger: merges, deduplicates, and sorts entries
  • Writer: writes normalized .gitignore file
• Updated SyncCommand to orchestrate .gitignore synchronization
• Entries are sorted: directories first, then files, alphabetical within each group

Changes

• Created src/GitIgnore/Reader.php - reads .gitignore entries
• Created src/GitIgnore/Classifier.php - classifies entries as directory/file
• Created src/GitIgnore/Merger.php - merges and sorts entries
• Created src/GitIgnore/Writer.php - writes normalized output
• Updated SyncCommand to call syncGitIgnore() method
• Created src/Command/GitIgnoreCommand.php - standalone command for .gitignore operations
• Added comprehensive PHPDoc documentation to all GitIgnore classes (interface, implementation, command, and tests)
• Updated README.md to include new gitignore command
• Updated Sphinx documentation with new command reference

Architecture

The implementation follows the acceptance criteria requirements:

1. Separate dedicated classes - Each responsibility is isolated in its own class
2. Command as orchestrator - The command layer only orchestrates, no core logic
3. Loose coupling - Classes can be reused by other commands/tools/packages
4. Deterministic output - Always sorted: directories first, then files, alphabetically

Example

If dev-tools has:
.idea/ .vscode/ vendor/ .DS_Store *.cache

And project has:
tmp/ vendor/ composer.lock

The synced result will be:
.idea/ tmp/ vendor/ .vscode/ *.cache .DS_Store composer.lock

New Command

The gitignore command can be used standalone:

# Merge and sync .gitignore files
composer dev-tools gitignore

# Specify custom source and target paths
composer dev-tools gitignore -- --source=/path/to/source/.gitignore --target=/path/to/target/.gitignore

Testing

All tests pass (125 tests, 306 assertions) with 85.89% code coverage.

Closes #12