Fix .dms.json not found when working directory differs from media path

[Copilot]

After Init(), RootObjectPath is reset to "./" while FS is rooted at the actual media path. readDynamicStream was using ioutil.ReadFile which resolves relative to the process working directory — so .dms.json files were only found when the working directory happened to match the media root.

Changes

• readDynamicStream: accepts an fs.FS parameter; uses fs.ReadFile(fsys, path) instead of ioutil.ReadFile(path)
• cds.go / dms.go: pass me.FS / server.FS at each call site — this FS is always rooted at the correct media directory regardless of working directory
• Removes now-unused io/ioutil import from cds.go

• Fixes .dms.json not found if working directory != media path #187