feat(shared): add shared utilities for command and skill loading

- frontmatter.ts: YAML frontmatter parser
- file-reference-resolver.ts: resolve @file references in markdown
- command-executor.ts: execute shell commands in markdown
- model-sanitizer.ts: sanitize model names for OpenCode compatibility

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

src/shared/file-reference-resolver.ts

@@ -0,0 +1,85 @@
+import { existsSync, readFileSync, statSync } from "fs"
+import { join, isAbsolute } from "path"
+
+interface FileMatch {
+  fullMatch: string
+  filePath: string
+  start: number
+  end: number
+}
+
+const FILE_REFERENCE_PATTERN = /@([^\s@]+)/g
+
+function findFileReferences(text: string): FileMatch[] {
+  const matches: FileMatch[] = []
+  let match: RegExpExecArray | null
+
+  FILE_REFERENCE_PATTERN.lastIndex = 0
+
+  while ((match = FILE_REFERENCE_PATTERN.exec(text)) !== null) {
+    matches.push({
+      fullMatch: match[0],
+      filePath: match[1],
+      start: match.index,
+      end: match.index + match[0].length,
+    })
+  }
+
+  return matches
+}
+
+function resolveFilePath(filePath: string, cwd: string): string {
+  if (isAbsolute(filePath)) {
+    return filePath
+  }
+  return join(cwd, filePath)
+}
+
+function readFileContent(resolvedPath: string): string {
+  if (!existsSync(resolvedPath)) {
+    return `[file not found: ${resolvedPath}]`
+  }
+
+  const stat = statSync(resolvedPath)
+  if (stat.isDirectory()) {
+    return `[cannot read directory: ${resolvedPath}]`
+  }
+
+  const content = readFileSync(resolvedPath, "utf-8")
+  return content
+}
+
+export async function resolveFileReferencesInText(
+  text: string,
+  cwd: string = process.cwd(),
+  depth: number = 0,
+  maxDepth: number = 3
+): Promise<string> {
+  if (depth >= maxDepth) {
+    return text
+  }
+
+  const matches = findFileReferences(text)
+  if (matches.length === 0) {
+    return text
+  }
+
+  const replacements = new Map<string, string>()
+
+  for (const match of matches) {
+    const resolvedPath = resolveFilePath(match.filePath, cwd)
+    const content = readFileContent(resolvedPath)
+    replacements.set(match.fullMatch, content)
+  }
+
+  let resolved = text
+  for (const [pattern, replacement] of replacements.entries()) {
+    resolved = resolved.split(pattern).join(replacement)
+  }
+
+  if (findFileReferences(resolved).length > 0 && depth + 1 < maxDepth) {
+    return resolveFileReferencesInText(resolved, cwd, depth + 1, maxDepth)
+  }
+
+  return resolved
+}