fix: preserve trusted request identities in audit evidence

[tuzuminami]

Summary

• generate a server-owned request ID at ingress and keep caller correlation separate
• persist the trusted request ID through decision receipts, audit events, replay evidence, and PostgreSQL migration 003
• record idempotent replays with the current transport request ID without mutating the original receipt or duplicating outbox events

Closes #27

Verification

• pnpm run verify
• PostgreSQL integration cases are present but skipped locally because VEIL_TEST_DATABASE_URL is not configured.