spec: add truth-plane OpenAPI/AsyncAPI patch files

[mdheller]

Adds additive patch fragments for the Truth Plane:

• openapi.truth-plane.patch.yaml (truth surfaces, delta surfaces, incident events)
• asyncapi.truth-plane.patch.yaml (truth/delta/incident channels)

These patches follow the existing additive patch strategy used for the agent plane and keep the base specs unchanged.

[mdheller]

Notes for reviewers / merge order:

1. This patch references schemas/control-plane/incident-events.schema.json from the OpenAPI patch. That schema is introduced in PR spec: add incident event schema + truth/delta surface examples #18 (incident schema + truth/delta examples). Please merge spec: add incident event schema + truth/delta surface examples #18 first (or treat spec: add truth-plane OpenAPI/AsyncAPI patch files #27 as dependent on spec: add incident event schema + truth/delta surface examples #18).

2. Event spine typing: all AsyncAPI truth/delta/incident channels use EventEnvelope as the message payload wrapper. Concretely:

• EventEnvelope.eventType is one of: TruthSurfaceUpserted, DeltaSurfaceRecorded, IncidentFreezeRecorded|IncidentForkRecorded|IncidentKillRecorded.
• EventEnvelope.objectId is the URN of the domain object (urn:srcos:truth-surface:*, urn:srcos:delta-surface:*, or incident event id/URN if we add one).
• EventEnvelope.payload contains the full domain object (TruthSurface / DeltaSurface / IncidentEvent) conforming to the referenced JSON Schema.

This keeps transport uniform while allowing domain objects to evolve independently.

[mdheller]

Update: repo auto-merge is disabled and the connector merge action is currently failing. To keep momentum, we manually landed the two patch files directly on main:

• openapi.truth-plane.patch.yaml
• asyncapi.truth-plane.patch.yaml

These were copied verbatim from branch spec/truth-plane-patches-20260415.

Next: this PR can be closed as already applied (or kept open until maintainers confirm).