Improve public recall eval case quality

[sheawinkler]

Summary

• generate saved recall eval cases from concrete live memory docs before broad topic rollups
• scope generated cases to the owning project and one expected file
• keep rollup fallback for empty stores

Verification

• GOCACHE=/Volumes/wd_black/codex_go_cache GOMODCACHE=/Volumes/wd_black/codex_gomod_cache go test . -run 'TestProxyForwardsBatchAndOpsQueuePaths|TestRecallEvalCasesRefreshUsesLiveFileBackedMemory|TestMemoryRecallEvaluateSaved(IsGoNative|ScoresGraphContribution)' -count=1
• GOCACHE=/Volumes/wd_black/codex_go_cache GOMODCACHE=/Volumes/wd_black/codex_gomod_cache go test . -count=1