feat(tui): add shell and editor actions for selected workspace

[BalduinLandolt]

Summary

When selecting a workspace in loom tui, there should be actions to open a shell or editor in that workspace — mirroring loom shell and the proposed loom editor command (see related issue).

Motivation

loom shell is available from the CLI but not from the TUI. Since the TUI is the interactive way to manage workspaces, it's a natural place to offer quick actions like opening a shell or editor for the selected workspace. Currently you have to exit the TUI and run loom shell <name> separately.

Commands affected

• loom init
• loom new
• loom add
• loom remove
• loom down
• loom list
• loom status
• loom exec
• loom shell
• loom save
• loom open
• loom registry
• TUI
• New command

Modules affected

• tui
• workspace
• config

Proposed behavior

When a workspace is selected in the TUI, offer keybindings to:

• Open a shell in the workspace (equivalent to loom shell)
• Open the workspace in the configured editor (equivalent to loom editor, once that feature exists)

Acceptance criteria

• TUI exposes a "shell" action for the selected workspace
• TUI exposes an "editor" action once loom editor is implemented
• Actions use the same [terminal] and [editor] config as the CLI commands