feat: improve OwnerAdmin array fields and speed up changelist

[thomasrockhu-codecov]

Summary

Improvements to the Django OwnerAdmin (codecov_auth/admin.py), split out onto a fresh branch off main:

• Fixes a severe changelist slowdown. The repository_count column was built with a Count("repository", distinct=True) annotation, which added a LEFT JOIN repos ... GROUP BY ownerid to the changelist queryset. Django's paginator then wrapped that in SELECT COUNT(*) FROM (... GROUP BY ownerid) subquery, scanning the full owners×repos space on every page load. Sentry showed this single query at p50 ≈ 11.6 s / p95 ≈ 14.4 s, accounting for ~77% of all DB time on the page (page p95 ≈ 32 s, p99 ≈ 52 s).
  • Replaced it with a correlated Subquery (Coalesced to 0) so there is no GROUP BY on the outer query — the paginator count collapses to a plain SELECT COUNT(*) FROM owners, and the per-row repo count only runs for the ~100 displayed rows.
  • Set show_full_count = False to skip even that unfiltered count on the landing view.
• Renders the admins / organizations / permission owner-id array fields as read-only lists of links to the related admin pages, so staff can see who each id refers to and jump straight to them.

Investigation

Root-caused via Sentry (production, codecov/api): the Owner changelist transaction spent ~88% of wall time in db spans, dominated by the paginator count query above.

Test plan

• pytest codecov_auth/tests/test_admin.py::OwnerAdminTest (added test_get_queryset_annotates_repository_count; existing array-field display tests included).
• After deploy, re-check the Sentry breakdown for the Owner changelist — the SELECT COUNT(*) FROM (... GROUP BY ownerid) query should be gone and p50/p95 should drop toward sub-second.

Notes

• Commit also present on th/admin-owner-id-array-fields (PR feat: add RBAC (Viewer/Member/Admin) to Django admin #1398); this branch isolates it against main.

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[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.89%. Comparing base (701e991) to head (6112e79).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/codecov_auth/admin.py	97.36%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1405   +/-   ##
=======================================
  Coverage   91.89%   91.89%           
=======================================
  Files        1325     1325           
  Lines       50868    50905   +37     
  Branches     1626     1626           
=======================================
+ Hits        46744    46780   +36     
- Misses       3818     3819    +1     
  Partials      306      306           

Flag	Coverage Δ
apiunit	94.94% <97.36%> (+<0.01%)	⬆️

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[codecov-notifications]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/codecov_auth/admin.py	97.36%	1 Missing ⚠️

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[thomasrockhu-codecov]

Superseded by the split PRs: #1406 (changelist count-query performance fix) and #1407 (owner-id array-field display). Closing this combined PR in favor of the two focused ones.