fix: address Greptile review — frontmatter, CI safety, null guards

Greptile fixes:
- Removed non-standard YAML frontmatter fields (observe, feedback, rollback) from all 4 skills — only name, description, origin, version per CONTRIBUTING.md
- Added null guard to checkInteractions implementation (was missing despite test)
- CI: replaced 2>/dev/null with 2>&1 (was silencing safety-critical errors)
- CI: quoted $RESULT variable (was breaking jq on JSON with spaces)
- CI: added division-by-zero guard when test suite is empty
- CI: added note that Jest is reference implementation, thresholds are framework-agnostic

skills/healthcare-cdss-patterns/SKILL.md

@@ -3,9 +3,6 @@ name: healthcare-cdss-patterns
 description: Clinical Decision Support System (CDSS) development patterns. Drug interaction checking, dose validation, clinical scoring (NEWS2, qSOFA), alert severity classification, and integration into EMR workflows.
 origin: Health1 Super Speciality Hospitals — contributed by Dr. Keyur Patel
 version: "1.0.0"
-observe: "PostToolUse"
-feedback: "manual"
-rollback: "git revert"
 ---
 
 # Healthcare CDSS Development Patterns
@@ -60,6 +57,7 @@ function checkInteractions(
   currentMedications: string[],
   allergyList: string[]
 ): InteractionAlert[] {
+  if (!newDrug) return [];
   const alerts: InteractionAlert[] = [];
   for (const current of currentMedications) {
     const interaction = findInteraction(newDrug, current);