[did2 #15] Release notes, deprecation timeline, version bump

[stevevanhooser]

Part of the NDI-matlab did2 migration. Target branch: Vnext (last issue before main-merge).

Scope

Publish a clear horizon so customers can plan upgrades.

• Choose target release version (e.g., NDI 4.0.0). Discuss with maintainer.
• Update Contents.m / version files in NDI-matlab as appropriate.
• Release notes covering the migration: what V_delta is, what changed, link to the migration guide (issue 14).
• Deprecation table:
  • v1 writes deprecated in this release (4.0.0); compat layer translates legacy alias writes to V_delta on the wire.
  • v1 reads remain supported in 4.x.
  • v1 reads removed in 5.0 (target N months later — pick a horizon).
  • Compat layer (+ndi/+compat/) removed alongside v1 read support.

Out of scope

Actually removing v1 read support — that's a future release.

Dependencies

Everything else. This is the final issue, immediately before the Vnext → main merge PR.