XY-836: [ELF prod gate] Run full comparison and production adoption decision

[yvette-carlisle]

Summary

• Add the June 9, 2026 production adoption gate report with the verdict: ready for personal production use with bounded caveats.
• Update README and the benchmarking index so public claims match the fresh encoded evidence and private-corpus limitation.
• Fix two benchmark runner issues found during the gate: Docker builds without git metadata now get a VERGEN_GIT_SHA fallback, and baseline-backfill-docker resolves defaults inside the shell.

Fresh Evidence

• cargo make baseline-production-private failed closed at the missing ELF_BASELINE_PRODUCTION_CORPUS_MANIFEST guard; no private-corpus pass is claimed.
• live-baseline-20260609083644: production-synthetic provider run, 8 docs, 6 queries, 8/8 checks, pass in 59 seconds.
• live-baseline-20260609083814: all-project smoke run with typed external adapter states; ELF and qmd passed, while other adapters retained lifecycle, incomplete, or wrong-result states.
• live-baseline-20260609090719: provider stress run, 480 docs, 16 queries, 9/9 checks, pass in 779 seconds.
• live-baseline-20260609092144: provider backfill run, 2,000 docs, resume 1,000 -> 2,000, zero duplicate source notes, 9/9 checks, pass in 2,804 seconds.
• Single-user restore proof rebuilt Qdrant from Postgres-held vectors with rebuilt_count=1, missing_vector_count=0, error_count=0, and recovered searchable results.

Validation

• cargo make baseline-live-docker-clean
• cargo make fmt
• cargo make lint-fix
• cargo make checks