fix: add 'built-in' to SkillMetadata source type

Author: hannesrudolph

packages/types/src/skills.ts

@@ -5,8 +5,8 @@
 export interface SkillMetadata {
 	name: string // Required: skill identifier
 	description: string // Required: when to use this skill
-	path: string // Absolute path to SKILL.md
-	source: "global" | "project" // Where the skill was discovered
+	path: string // Absolute path to SKILL.md (or "<built-in:name>" for built-in skills)
+	source: "global" | "project" | "built-in" // Where the skill was discovered
 	mode?: string // If set, skill is only available in this mode
 }