Fixes GRN-4913

Summary by CodeRabbit

• New Features

  • Environments: adds an Environments view, picker, notebook↔environment mapping, per-environment lifecycle, server control, venv/toolkit management, multi-step create flow, and commands for create/start/stop/restart/delete/rename/manage-packages/refresh/select-for-notebook.

• UI

  • Tree view with status visuals; kernel display names and server labels include environment info and ports; environment command titles localized; output channel shown by default.

• Tests

  • Extensive unit tests for environment manager, storage, view, picker, tree items, activation, auto-selector rebuild, and related flows.

• Documentation

  • Expanded contributor guide and new debugging guide.

• Chores

  • Added runtime uuid dependency; removed @types/uuid dev dependency.