feat(skill-loader): add async directory scanner

Add async versions of skill loading functions with concurrency control:
- mapWithConcurrency: Generic concurrent mapper with limit (16)
- loadSkillFromPathAsync: Async skill file parsing
- loadMcpJsonFromDirAsync: Async mcp.json loading
- discoverSkillsInDirAsync: Async directory scanner

Tests: 20 new tests covering all async functions

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

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

@@ -0,0 +1,178 @@
+import { readFile, readdir } from "fs/promises"
+import type { Dirent } from "fs"
+import { join, basename } from "path"
+import yaml from "js-yaml"
+import { parseFrontmatter } from "../../shared/frontmatter"
+import { sanitizeModelField } from "../../shared/model-sanitizer"
+import { resolveSymlink, isMarkdownFile } from "../../shared/file-utils"
+import type { CommandDefinition } from "../claude-code-command-loader/types"
+import type { SkillScope, SkillMetadata, LoadedSkill } from "./types"
+import type { SkillMcpConfig } from "../skill-mcp-manager/types"
+
+export async function mapWithConcurrency<T, R>(
+  items: T[],
+  mapper: (item: T) => Promise<R>,
+  concurrency: number
+): Promise<R[]> {
+  const results: R[] = new Array(items.length)
+  let index = 0
+  
+  const worker = async () => {
+    while (index < items.length) {
+      const currentIndex = index++
+      results[currentIndex] = await mapper(items[currentIndex])
+    }
+  }
+  
+  const workers = Array.from({ length: Math.min(concurrency, items.length) }, () => worker())
+  await Promise.all(workers)
+  
+  return results
+}
+
+function parseSkillMcpConfigFromFrontmatter(content: string): SkillMcpConfig | undefined {
+  const frontmatterMatch = content.match(/^---\r?\n([\s\S]*?)\r?\n---/)
+  if (!frontmatterMatch) return undefined
+
+  try {
+    const parsed = yaml.load(frontmatterMatch[1]) as Record<string, unknown>
+    if (parsed && typeof parsed === "object" && "mcp" in parsed && parsed.mcp) {
+      return parsed.mcp as SkillMcpConfig
+    }
+  } catch {
+    return undefined
+  }
+  return undefined
+}
+
+export async function loadMcpJsonFromDirAsync(skillDir: string): Promise<SkillMcpConfig | undefined> {
+  const mcpJsonPath = join(skillDir, "mcp.json")
+
+  try {
+    const content = await readFile(mcpJsonPath, "utf-8")
+    const parsed = JSON.parse(content) as Record<string, unknown>
+    
+    if (parsed && typeof parsed === "object" && "mcpServers" in parsed && parsed.mcpServers) {
+      return parsed.mcpServers as SkillMcpConfig
+    }
+    
+    if (parsed && typeof parsed === "object" && !("mcpServers" in parsed)) {
+      const hasCommandField = Object.values(parsed).some(
+        (v) => v && typeof v === "object" && "command" in (v as Record<string, unknown>)
+      )
+      if (hasCommandField) {
+        return parsed as SkillMcpConfig
+      }
+    }
+  } catch {
+    return undefined
+  }
+  return undefined
+}
+
+export async function loadSkillFromPathAsync(
+  skillPath: string,
+  resolvedPath: string,
+  defaultName: string,
+  scope: SkillScope
+): Promise<LoadedSkill | null> {
+  try {
+    const content = await readFile(skillPath, "utf-8")
+    const { data, body } = parseFrontmatter<SkillMetadata>(content)
+    const frontmatterMcp = parseSkillMcpConfigFromFrontmatter(content)
+    const mcpJsonMcp = await loadMcpJsonFromDirAsync(resolvedPath)
+    const mcpConfig = mcpJsonMcp || frontmatterMcp
+
+    const skillName = data.name || defaultName
+    const originalDescription = data.description || ""
+    const isOpencodeSource = scope === "opencode" || scope === "opencode-project"
+    const formattedDescription = `(${scope} - Skill) ${originalDescription}`
+
+    const wrappedTemplate = `<skill-instruction>
+Base directory for this skill: ${resolvedPath}/
+File references (@path) in this skill are relative to this directory.
+
+${body.trim()}
+</skill-instruction>
+
+<user-request>
+$ARGUMENTS
+</user-request>`
+
+    const definition: CommandDefinition = {
+      name: skillName,
+      description: formattedDescription,
+      template: wrappedTemplate,
+      model: sanitizeModelField(data.model, isOpencodeSource ? "opencode" : "claude-code"),
+      agent: data.agent,
+      subtask: data.subtask,
+      argumentHint: data["argument-hint"],
+    }
+
+    return {
+      name: skillName,
+      path: skillPath,
+      resolvedPath,
+      definition,
+      scope,
+      license: data.license,
+      compatibility: data.compatibility,
+      metadata: data.metadata,
+      allowedTools: parseAllowedTools(data["allowed-tools"]),
+      mcpConfig,
+    }
+  } catch {
+    return null
+  }
+}
+
+function parseAllowedTools(allowedTools: string | undefined): string[] | undefined {
+  if (!allowedTools) return undefined
+  return allowedTools.split(/\s+/).filter(Boolean)
+}
+
+export async function discoverSkillsInDirAsync(skillsDir: string): Promise<LoadedSkill[]> {
+  try {
+    const entries = await readdir(skillsDir, { withFileTypes: true })
+    
+    const processEntry = async (entry: Dirent): Promise<LoadedSkill | null> => {
+      if (entry.name.startsWith(".")) return null
+
+      const entryPath = join(skillsDir, entry.name)
+
+      if (entry.isDirectory() || entry.isSymbolicLink()) {
+        const resolvedPath = resolveSymlink(entryPath)
+        const dirName = entry.name
+
+        const skillMdPath = join(resolvedPath, "SKILL.md")
+        try {
+          await readFile(skillMdPath, "utf-8")
+          return await loadSkillFromPathAsync(skillMdPath, resolvedPath, dirName, "opencode-project")
+        } catch {
+          const namedSkillMdPath = join(resolvedPath, `${dirName}.md`)
+          try {
+            await readFile(namedSkillMdPath, "utf-8")
+            return await loadSkillFromPathAsync(namedSkillMdPath, resolvedPath, dirName, "opencode-project")
+          } catch {
+            return null
+          }
+        }
+      }
+
+      if (isMarkdownFile(entry)) {
+        const skillName = basename(entry.name, ".md")
+        return await loadSkillFromPathAsync(entryPath, skillsDir, skillName, "opencode-project")
+      }
+
+      return null
+    }
+
+    const skillPromises = await mapWithConcurrency(entries, processEntry, 16)
+    return skillPromises.filter((skill): skill is LoadedSkill => skill !== null)
+  } catch (error: unknown) {
+    if (error && typeof error === "object" && "code" in error && error.code === "ENOENT") {
+      return []
+    }
+    return []
+  }
+}