Adds a diagnostic check that discovers and reports custom types
used by child repos in multi-repo setups. This is the 'discover'
part of the 'trust + discover' pattern for federation.
The check:
- Lists custom types found in each child repo's config/DB
- Warns about hydrated issues using types not found anywhere
- Is informational only (doesn't fail overall doctor check)
Part of epic: bd-9ji4z
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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