perf(sync): bulk upsert synced reviews

[thomasorgeval]

Summary

• Replaces per-review upserts during store sync with one bulk insert ... on conflict do update, while keeping returned storedCount and newReviewIds semantics for normal unique store review payloads.
• Deduplicates repeated external review IDs before the bulk upsert so a malformed page cannot make Postgres reject the statement for touching the same conflict target twice.
• Internal Postgres benchmark for 500 synced reviews improved median insert/upsert time from 547.5ms to 120.9ms over 5 iterations.

Expected impact

• Store sync review persistence should issue far fewer database round trips for each fetched page, reducing sync latency and database overhead as review batches grow.
• Duplicate external IDs in one fetched batch are collapsed to the last occurrence instead of being written repeatedly. This avoids a bulk-upsert conflict failure and should not affect normal store API payloads.

Verification

• NX_DAEMON=false /home/thomas/.local/bin/mise exec node@24 -- pnpm nx typecheck sync --skip-nx-cache --tui=false
• NX_DAEMON=false /home/thomas/.local/bin/mise exec node@24 -- pnpm nx test sync --skip-nx-cache --tui=false
• NX_DAEMON=false /home/thomas/.local/bin/mise exec node@24 -- pnpm exec biome lint packages/sync/src/review-storage.ts
• Benchmark command: NODE_PATH=/home/thomas/projects/reviewinbox/node_modules DATABASE_URL=<local postgres> /home/thomas/.local/bin/mise exec node@24 -- pnpm tsx /home/thomas/.hermes/autonomous-coding/runs/20260621T060050Z/benchmarks/sync-review-storage/bench.ts

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