fix: move SKILL.md to .github/skills/ so /skills add works

The /skills add command expects SKILL.md at .github/skills/<name>/SKILL.md.
Previously it was at .github/copilot/skills/<name>/SKILL.md as a symlink,
which GitHub cannot resolve when fetching raw content.

- Replaced symlink with actual SKILL.md file at correct path
- Removed old .github/copilot/skills/ directory
- Updated README project structure to match

Author: web-flow