* fix(#2991): route /gsd command output through Pi's display shape
The registerCommand('gsd') handler returned a bare string, which Pi's
ExtensionAPI does not display. Changed all return paths to Pi's structured
{ content: [{ type: 'text', text }] } shape, matching the gsd_invoke tool's
proven output contract. Updated 2 reachability tests that asserted the old
bare-string return shape.
* chore(#2991): backfill changeset PR number 3097
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Co-authored-by: sim <sim@local>
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