refactor(claude-code-plugin-loader): split loader.ts into per-type loaders

Extract plugin component loading into dedicated modules:
- discovery.ts: plugin directory detection
- plugin-path-resolver.ts: path resolution logic
- agent-loader.ts, command-loader.ts, hook-loader.ts
- mcp-server-loader.ts, skill-loader.ts

src/features/claude-code-plugin-loader/plugin-path-resolver.ts

@@ -0,0 +1,23 @@
+const CLAUDE_PLUGIN_ROOT_VAR = "${CLAUDE_PLUGIN_ROOT}"
+
+export function resolvePluginPath(path: string, pluginRoot: string): string {
+  return path.replace(CLAUDE_PLUGIN_ROOT_VAR, pluginRoot)
+}
+
+export function resolvePluginPaths<T>(obj: T, pluginRoot: string): T {
+  if (obj === null || obj === undefined) return obj
+  if (typeof obj === "string") {
+    return resolvePluginPath(obj, pluginRoot) as T
+  }
+  if (Array.isArray(obj)) {
+    return obj.map((item) => resolvePluginPaths(item, pluginRoot)) as T
+  }
+  if (typeof obj === "object") {
+    const result: Record<string, unknown> = {}
+    for (const [key, value] of Object.entries(obj)) {
+      result[key] = resolvePluginPaths(value, pluginRoot)
+    }
+    return result as T
+  }
+  return obj
+}