perf(client): a repository identity refresh keeps unchanged projects identical - #20730

Eligibility
This is a narrowly scoped client performance fix that preserves project data while reusing objects for structurally unchanged repository identities, preventing unnecessary subscriber re-renders. The behavior is covered by a focused unit test and introduces no product-default, static-analysis, schema, or infrastructure changes.

Notes:
No code owners found in target merge base 70d60e0