Use new skill registration system

[JosXa]

anomalyco/opencode#9640 introduced a new skill registration system that makes our "copy the skill to the user's global config" obsolete. We need to use the new mechanism instead.

@opencode-agent please create a PR

[JosXa]

I've implemented the changes to adopt the new skill registration system from OpenCode PR #9640.

Changes made:

• The plugin now registers its skill folder path via skills.paths in the config hook instead of copying SKILL.md to ~/.config/opencode/skill/snippets/
• Removed the installSkill config option and installSkillToGlobal function (no longer needed)
• Updated tests and documentation accordingly

All 179 tests pass and biome check is clean.

PR: #23

Note: This PR requires OpenCode PR #9640 to be merged first for the skills.paths feature to work. The implementation uses type assertion to handle the new property that doesn't exist in the current SDK types yet.

[JosXa]

PR #23 is ready to merge.

Status:

• All 179 tests pass
• Biome check is clean
• PR is marked as "MERGEABLE"
• Both review comments have been addressed:
  1. ✅ Redundant comment removed
  2. ✅ Bundling concern clarified (standard tsc compilation, not bundling)

The PR correctly implements the new skill registration system by using skills.paths in the config hook instead of copying SKILL.md files. Ready for final approval and merge.