fix(matchmaking): harden two-person production flow

[Ltcc0]

Summary

• make structured JSON requests compatible with the production LLM gateway
• normalize provider quirks without bypassing match/activity validation
• deterministically select the sole compatible activity for an exact two-person pool, while keeping the quality judge
• normalize test-pool timestamps and non-option product messages

Verification

• pnpm --filter @tomeet/data typecheck
• pnpm --filter @tomeet/intelligence typecheck
• pnpm --filter @tomeet/intelligence test (59 passed)
• production smoke test confirmed two requests enter the same round; current pair was rated acceptable with one isolation risk, so no offer was created under the existing good/excellent threshold