feat: add first-party skills, ponytail lock, and full lint suite

- add ponytail skill set to skills-lock.json (14 locked skills total)
- add first-party medusa skill under skills/, layered on install
- make test now runs ruff, shellcheck, and markdownlint-cli2
- CI installs the lint tools before make test in both workflows
- MIT license, funding buttons, thanks and donation sections in README
- .markdownlint-cli2.jsonc config; ignore lint caches in .gitignore

.gitignore

@@ -1,8 +1,21 @@
+# Python
 .venv/
-dist/
-build/
 __pycache__/
 *.pyc
+dist/
+build/
+.ruff_cache/
+.pytest_cache/
+.mypy_cache/
+
+# Node
+node_modules/
+npm-debug.log*
+
+# Rendered skill install targets
 .agents/
 .claude/
-node_modules/
+
+# Editor / OS
+.DS_Store
+*.swp