contracts: add sourceos-shell OpenAPI and AsyncAPI surfaces

[mdheller]

Summary

Stacked on top of the sourceos-shell contract schema work, this PR adds the first API/event patch surfaces for shell artifact, annotation, run/report, and publish/mirror workflows.

Updated files

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

Added OpenAPI paths

• /v2/artifacts/manifest
• /v2/artifacts/signature
• /v2/artifacts/validation
• /v2/annotations/export
• /v2/runs/report
• /v2/diagnostics/noether
• /v2/publish/decisions
• /v2/mirror/receipts

Added AsyncAPI channels

• srcos.v2.artifact.events
• srcos.v2.annotation.events
• srcos.v2.run.events
• srcos.v2.publish.events

Why

The schema layer is now present for artifact, annotation, run/report, diagnostic, publish, and mirror objects. This PR extends the additive API and event patch files so downstream implementations have a defined backlog-compatible integration surface.

Stack relationship

This PR is stacked on top of:

• sourceos-spec#33
• sourceos-spec#50

Follow-on

• tighten operation response payloads
• bind eventType guidance more explicitly in EventEnvelope examples
• generate bindings for downstream runtime consumption once sourceos-shell exists

[mdheller]

Stack note:

This PR sits on top of the current sourceos-shell contract chain:

• base: contracts: bootstrap sourceos-shell artifact, PDF, search, and comment schemas #33 — initial artifact/PDF/search/comment schemas
• then: contracts: add annotation, run, Noether, publish, and mirror schemas #50 — annotation/run/Noether/publish/mirror schemas
• this PR: contracts: add sourceos-shell OpenAPI and AsyncAPI surfaces #52 — OpenAPI/AsyncAPI surfaces for those objects

The remaining blocker outside this repo is creation of SourceOS-Linux/sourceos-shell itself, which is currently tracked downstream in the Linux realization repo. Once that product/runtime repo exists, generated bindings from this stack should become the source of truth for runtime consumption.