fix: resolve SKILL.md validation errors

skills/referral-program/SKILL.md

@@ -1,6 +1,8 @@
 ---
 name: referral-program
 description: "When the user wants to create, optimize, or analyze a referral program, affiliate program, or word-of-mouth strategy. Also use when the user mentions 'referral,' 'affiliate,' 'ambassador,' 'word of..."
+risk: unknown
+source: community
 ---
 
 # Referral & Affiliate Programs
@@ -600,3 +602,6 @@ If you need more context:
 - **marketing-psychology**: For understanding referral motivation
 - **analytics-tracking**: For tracking referral attribution
 - **pricing-strategy**: For structuring rewards relative to LTV
+
+## When to Use
+This skill is applicable to execute the workflow or actions described in the overview.