refactor: rename repoAtUri for accuracy
* Repos are identified by their DID now, hence the name change
* Update tests accordingly
* Consolidate @atproto/identity usage into pds-resolver.ts by moving
resolveHandleToDid there; at-uri.ts re-exports it and no longer
imports @atproto/identity directly
Co-authored-by: Claude (claude-sonnet-4-6) <noreply@anthropic.com>
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