Move skills to .ai/skills/ for tool-agnostic discoverability

Moves the canonical skill definitions from .claude/skills/ to .ai/skills/
and replaces .claude/skills with a symlink, so Claude Code still discovers
them while other AI agents can find them in a tool-neutral location.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

.claude/skills/check-upstream/SKILL.md .ai/skills/check-upstream/SKILL.md.claude/skills/check-upstream/SKILL.md renamed to .ai/skills/check-upstream/SKILL.md

@@ -0,0 +1 @@
+../.ai/skills