Use authenticated installation metadata for repository coverage #410

🤖 Generated by the Agentic Engineer

The live coverage client asks the repository-list endpoint for installation selection. The documented response contains repository pages and total count; selection belongs to authenticated installation metadata. A fixture returning the requested field masked the mismatch.

Acceptance:

• Read and verify the installation metadata through the existing authenticated App proof, then validate every repository page and stable totals.
• Share the proof with the admin-team auditor so the two clients use one installation/census contract.
• Preserve UNKNOWN for missing, selected, malformed, suspended or changing evidence; keep diagnostics private.
• Test the actual API path using the documented response shape, and verify the merged main workflow.

Part of #84; repair is included in draft #409 before routine activation. Rough size: M. Priority: P1.