Look for assets in subdirectories

Fixes #503.

When running `npm start` the README.skills.md file will be updated to
include any newly-added skills. This includes the name and description
from the skill's frontmatter, but also a list of assets in the skill--
that is, files other than SKILL.md.

However, the code in yaml-parser.mjs to enumerate the asset files only
looks in the immediate skill directory, not any subdirectories. Those
files will be missing from README.skills.md.

Here we update yaml-parser.mjs to recurse through the subdirectories as
well.

eng/yaml-parser.mjs

@@ -161,14 +161,26 @@ function parseSkillMetadata(skillPath) {
         return null;
       }
 
-      // List bundled assets (all files except SKILL.md)
-      const assets = fs
-        .readdirSync(skillPath)
-        .filter((file) => {
-          const filePath = path.join(skillPath, file);
-          return file !== "SKILL.md" && fs.statSync(filePath).isFile();
-        })
-        .sort();
+      // List bundled assets (all files except SKILL.md), recursing through subdirectories
+      const getAllFiles = (dirPath, arrayOfFiles = []) => {
+        const files = fs.readdirSync(dirPath);
+
+        files.forEach((file) => {
+          const filePath = path.join(dirPath, file);
+          if (fs.statSync(filePath).isDirectory()) {
+            arrayOfFiles = getAllFiles(filePath, arrayOfFiles);
+          } else {
+            const relativePath = path.relative(skillPath, filePath);
+            if (relativePath !== "SKILL.md") {
+              arrayOfFiles.push(relativePath);
+            }
+          }
+        });
+
+        return arrayOfFiles;
+      };
+
+      const assets = getAllFiles(skillPath).sort();
 
       return {
         name: frontmatter.name,