feat(frontmatter): track parsing errors and frontmatter existence in result type

Add hadFrontmatter and parseError flags to FrontmatterResult interface to enable error handling in skill loading.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/shared/frontmatter.ts

@@ -3,6 +3,8 @@ import yaml from "js-yaml"
 export interface FrontmatterResult<T = Record<string, unknown>> {
   data: T
   body: string
+  hadFrontmatter: boolean
+  parseError: boolean
 }
 
 export function parseFrontmatter<T = Record<string, unknown>>(
@@ -12,7 +14,7 @@ export function parseFrontmatter<T = Record<string, unknown>>(
   const match = content.match(frontmatterRegex)
 
   if (!match) {
-    return { data: {} as T, body: content }
+    return { data: {} as T, body: content, hadFrontmatter: false, parseError: false }
   }
 
   const yamlContent = match[1]
@@ -22,8 +24,8 @@ export function parseFrontmatter<T = Record<string, unknown>>(
     // Use JSON_SCHEMA for security - prevents code execution via YAML tags
     const parsed = yaml.load(yamlContent, { schema: yaml.JSON_SCHEMA })
     const data = (parsed ?? {}) as T
-    return { data, body }
+    return { data, body, hadFrontmatter: true, parseError: false }
   } catch {
-    return { data: {} as T, body }
+    return { data: {} as T, body, hadFrontmatter: true, parseError: true }
   }
 }