Implement Core Plugin Engine (.orplug Manifest & Dynamic Registry)

[ClausValcaTD]

Implemented Core Plugin Engine (.orplug Manifest & Dynamic Registry) in OpenROM Core:

• Created PluginManifest model (core/lib/src/plugin/plugin_manifest.dart) for parsing and validating plugin.json.
• Implemented PluginRegistry (core/lib/src/plugin/plugin_registry.dart) and updated detector.dart to dynamically merge built-in format maps with active plugin extensions, platforms, colors, target formats, and command templates.
• Implemented PluginManager (core/lib/src/plugin/plugin_manager.dart) for per-user plugins storage resolution (~/.local/share/openrom/plugins/ / %APPDATA%\OpenROM\plugins\), ZIP extraction of .orplug archives, SHA256 checksum verification for platform binaries, executable permissions setup, and uninstallation.
• Updated Converter (core/lib/src/converter.dart) to route plugin conversions and resolve {bin} placeholders to absolute verified executable paths.
• Added CLI options (--install-plugin, --list-plugins, --remove-plugin) in openrom-core (core/bin/openrom.dart).
• Added unit tests in core/test/plugin_test.dart.

---

PR created automatically by Jules for task 17054072907669228202 started by @ClausValcaTD

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.