Update for netmd-js 4.x and Web MiniDisc Pro

[jaeming]

Why

Web MiniDisc Pro (the client at web.minidisc.wiki, and as far as I know the only client) now uses netmd-js 4.x and a codec-based format model. This server targets the older 3.x API, so against a current netmd-js it breaks — EKBOpenSource is no longer exported, MDSession resolves the EKB internally, and the track/format names changed. The net effect is that a fresh setup can't record with the current client.

This brings the server up to date. (Complements the client-side fix in asivery/webminidisc#99.)

Changes

• MDSession — drop the EKBOpenSource argument. In 4.x init() derives the EKB from the device's vendor/product IDs, so it's just new MDSession(device).
• Track converters — report SP as SPS (stereo) / SPM (mono) and MDLP as AT3 + bitrate, matching what the current client sends and renders.
• /upload — accept the SPS/SPM codec names the current client sends (both → PCM wireformat), and record SPM with DiscFormat.spMono.
• normalizeGroups — a blank disc comes back from netmd-js with an empty groups array; synthesize the "ungrouped" bucket the client expects, and make the group/track converters null-safe.
• package.json — depend on the published netmd-js@^4.4.1 instead of a local working tree. (Easy to revert to file: if you'd rather keep the working-tree workflow.)

Testing

Ran live against a Sony MZ-N505: /prepareUpload completes the EKB session handshake, disc listing / group rewrite work, and SP + LP2 uploads complete.

Notes

• Kept as a separate PR from the small /rewriteGroups + upload-lock bug fixes (Fix /rewriteGroups guard+await and release device lock on aborted upload #5), which are version-independent. There may be a trivial rebase where the two touch the /upload handler.

[jaeming]

Verification note — ran this branch's exact code against real hardware before opening:

• Installed the published netmd-js@4.4.1 (fresh npm install, not a local working tree) on a Raspberry Pi (Node 22) with a Sony MZ-N505 attached.
• Confirmed the named imports resolve under Node ESM against 4.4.1 (MDSession, DiscFormat, etc. all defined; DiscFormat.spMono = 4, Wireformat.pcm = 0).
• End-to-end against the deck:
  • /deviceName → Sony MZ-N505
  • /listContent → the updated converters emit the current codec model on real tracks ({codec:"AT3",bitrate:132} for MDLP, {codec:"SPS",bitrate:292} for SP)
  • /prepareUpload → new MDSession(device) + init() completes the EKB handshake
  • /finalizeUpload → clean close
• SP and LP2 uploads through the current Web MiniDisc Pro client complete end-to-end (via the companion client fix Fix stalled SP/mono upload over Remote NetMD webminidisc#99).

Note: kept separate from the version-independent /rewriteGroups + upload-lock fixes in #5; the two touch the /upload handler in different spots, so a trivial rebase may be needed depending on merge order. Happy to adjust anything (e.g. keep file:../netmd-js instead of pinning ^4.4.1).