Move AI gateway state source of truth from Redis to PostgreSQL - #5970

Summary

• read gateway routing config, provider-sync timestamps, and request-logging opt-ins from the PostgreSQL singleton tables added in Add database mirrors for AI gateway state #5965
• enforce request-logging opt-in mutations against a row-locked database record instead of Redis
• keep Redis compatibility mirrors for migrated state, using a 7-day TTL except for the existing 3-day stale-alert TTL
• serialize authoritative database mutations with their Redis mirrors so failed or concurrent writes cannot leave stale mirrors
• preserve three-day stale-sync reminders and normalize database timestamps at the API boundary

Verification

• formatted changed files with oxfmt
• git diff --check
• test, typecheck, and lint suites intentionally left to CI