feat(list): show all runtimes without argument and indicate global version

[CalvinAllen]

Description

The dtvem list command currently requires a runtime argument (e.g., dtvem list node). Users should be able to run dtvem list without arguments to see all installed versions across all runtimes.

Additionally, the command doesn't indicate which version is set as the global default.

Expected Behavior

• dtvem list (no args) shows all installed versions grouped by runtime
• Each version shows "(global)" indicator if it's the global default

Current Behavior

$ dtvem list
Error: accepts 1 arg(s), received 0

Acceptance Criteria

• dtvem list without arguments shows all installed versions
• Versions are grouped by runtime
• Global version is indicated with "(global)" suffix
• dtvem list <runtime> continues to work as before