Document four Interchange-boundary findings from the CL-7257 audit

[TheGreatAxios]

Consolidates PRs #525, #526, #527, #528 into one CI cycle — they were four independent docs files and strict branch protection made each one its own serialized merge.

Each doc records what was checked against the vendored pin a8bc06ae and what it concluded, so the same ground isn't re-derived later.

Doc	Ticket	Finding
workflow-deploy-source-vs-launch-spec.md	CL-7271	Opposite recovery models (freeze vs re-resolve). Adopting native would reverse CL-6687 and CL-6648. Not a duplicate.
workflow-freeze-vs-probe-gate.md	CL-7273	Composes the same native primitives by identity — same createDbFrozenApprovalWriter, same computeWireDefinitionHash. Not a reimplementation.
folded-mail-vs-intx-mailbox.md	CL-7276	Different storage planes: session_mail is Postgres, @intx/mailbox is IMAP-shaped over a git substrate with no Postgres dependency.
workflow-definition-access.md	CL-7275	41 hand-rolled queries categorised by access shape; routing them through the native store surfaced test fixtures asserting row shapes the database cannot produce.

Four of the six audit premises were wrong. The shared cause is recorded on CL-7257: they were generated by "a native export with zero callers next to a similarly-named product package", which cannot see the backing store, shared-by-identity composition, or deliberate divergence.

Docs only. No code change.