fix(media): clean expired files in subdirectories

cleanOldMedia() only scanned the top-level media directory, but
saveMediaBuffer() writes to subdirs (inbound/, outbound/, browser/).
Files in those subdirs were never cleaned up.

Now recurses one level into subdirectories, deleting expired files
while preserving the subdirectory folders themselves.

src/media/store.ts

@@ -88,6 +88,22 @@ export async function cleanOldMedia(ttlMs = DEFAULT_TTL_MS) {
   const mediaDir = await ensureMediaDir();
   const entries = await fs.readdir(mediaDir).catch(() => []);
   const now = Date.now();
+  const removeExpiredFilesInDir = async (dir: string) => {
+    const dirEntries = await fs.readdir(dir).catch(() => []);
+    await Promise.all(
+      dirEntries.map(async (entry) => {
+        const full = path.join(dir, entry);
+        const stat = await fs.stat(full).catch(() => null);
+        if (!stat || !stat.isFile()) {
+          return;
+        }
+        if (now - stat.mtimeMs > ttlMs) {
+          await fs.rm(full).catch(() => {});
+        }
+      }),
+    );
+  };
+
   await Promise.all(
     entries.map(async (file) => {
       const full = path.join(mediaDir, file);
@@ -95,7 +111,11 @@ export async function cleanOldMedia(ttlMs = DEFAULT_TTL_MS) {
       if (!stat) {
         return;
       }
-      if (now - stat.mtimeMs > ttlMs) {
+      if (stat.isDirectory()) {
+        await removeExpiredFilesInDir(full);
+        return;
+      }
+      if (stat.isFile() && now - stat.mtimeMs > ttlMs) {
         await fs.rm(full).catch(() => {});
       }
     }),