fix(skill): support YAML array format for allowed-tools field (#1163)

Fixes #1021

The allowed-tools field in skill frontmatter now supports both formats:
- Space-separated string: 'allowed-tools: Read Write Edit Bash'
- YAML array: 'allowed-tools: [Read, Write, Edit, Bash]'
- Multi-line YAML array format also works

Previously, skills using YAML array format would silently fail to parse,
causing them to not appear in the <available_skills> list.

Changes:
- Updated parseAllowedTools() in loader.ts, async-loader.ts, and merger.ts
  to handle both string and string[] types
- Updated SkillMetadata type to accept string | string[] for allowed-tools
- Added 4 test cases covering all allowed-tools formats

src/features/opencode-skill-loader/loader.ts

@@ -50,8 +50,15 @@ async function loadMcpJsonFromDir(skillDir: string): Promise<SkillMcpConfig | un
   return undefined
 }
 
-function parseAllowedTools(allowedTools: string | undefined): string[] | undefined {
+function parseAllowedTools(allowedTools: string | string[] | undefined): string[] | undefined {
   if (!allowedTools) return undefined
+  
+  // Handle YAML array format: already parsed as string[]
+  if (Array.isArray(allowedTools)) {
+    return allowedTools.map(t => t.trim()).filter(Boolean)
+  }
+  
+  // Handle space-separated string format: "Read Write Edit Bash"
   return allowedTools.split(/\s+/).filter(Boolean)
 }