refactor(bayn): use Effect evidence-store dates

[gregkonush]

Summary

• Replaces native Date construction in the evidence-store integration boundary with Effect DateTime and Clock.
• Preserves exact timestamp ordering and stale-expiry behavior without rule suppressions.
• Keeps this stack layer independently reviewable at 254 changed lines and bases directly on PR refactor(bayn): use Effect platform and date boundaries #13630.

Related Issues

None

Testing

• bunx tsc --noEmit --project services/bayn/tsconfig.json
• bun test src/db/evidence-store.integration.test.ts (73 PostgreSQL cases skipped locally because no test URL is configured)
• bun run lint
• bun run lint:oxlint
• bun run lint:oxlint:type
• bun run build
• Effect TSGo globalDate, globalDateInEffect, and unnecessaryArrowBlock diagnostics for the file: zero

Breaking Changes

None

Checklist

• Testing section documents the exact validation performed.
• Screenshots are not applicable and Breaking Changes is filled in.
• Documentation and follow-ups are unchanged or represented by later stack layers.

[gregkonush]