feat: reproducible agent skill collection with install/update tooling

- skills-lock.json pins every skill (extracted from infinito-nexus-core)
- make install (global to $HOME) and make project TARGET=<repo> copy the
  rendered skills into .agents/skills + .claude/skills
- make update refreshes the lock via npx skills; make test validates the
  lock shape and shellchecks the scripts
- CI: test workflow on push/PR, daily update workflow opening a PR
- MIRRORS for code.infinito.nexus and git.veen.world

.gitignore

@@ -3,3 +3,6 @@ dist/
 build/
 __pycache__/
 *.pyc
+.agents/
+.claude/
+node_modules/