gbrain v0.20+ changed `gbrain sources list --json` to return
{sources: [...]} instead of a flat array. sourceLocalPath crashed
upstream with `list.find is not a function` on every /sync-gbrain
invocation against modern gbrain. Accept both shapes for
forward/backward compat, matching probeSource/sourcePageCount in
lib/gbrain-sources.ts.
Contributed by @jakehann11 via #1571. Closes#1567. Supersedes #1564
(@tonyjzhou, same fix, different shape — credit retained).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>