fix(skills): frontmatter lint — using-interns v0.3.1 (YAML+≤1024), using-wiki-graph v0.1.1 (≤1024), ralph-loop-execution frontmatter, remove using-yt-tools stub, add scripts/lint-skills.py + wire into update.{sh,ps1}

scripts/update.sh

@@ -123,7 +123,10 @@ fi
 
 cd "$ROOT"
 info "Installing skills..."
-bash "$ROOT/scripts/install.sh"
+  # 0. Lint skills against Agent Skills spec (fail on violations)
+  python "$ROOT/scripts/lint-skills.py" "$ROOT/skills" || { error "SKILL.md lint failed - fix before install"; exit 1; }
+  # 1. Install all skills via install.sh
+  bash "$ROOT/scripts/install.sh"
 ok "Skills installed."
 
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