Print extension inventory as JSON

[jongio]

Problem

grut ext list and grut ext info only print fixed-width text. Extension authors and support scripts need a machine-readable inventory to check installed runtimes, enabled state, permissions, source URLs, and install paths.

Proposed solution

Add a --json flag to grut ext list and grut ext info. The JSON should use the same extension state already loaded by the manager.

Acceptance criteria

• grut ext list --json prints an array and prints [] when no extensions are installed.
• grut ext info <name> --json prints one extension object.
• The JSON includes name, version, runtime, enabled state, permissions, source URL, commit hash, install time, and directory.
• Existing text output stays unchanged when --json is not set.

Complexity

S

Priority

3