[v1.0] Publish JSON Schema artifacts for machine contracts

[codeforester]

Goal

Make base-cli's machine contracts consumable without importing Python.

Scope

• Publish versioned JSON Schema for success/error envelopes, inspection envelopes, logs, NDJSON records, and command-protocol payloads.
• Define required fields, optional fields, enum values, bounds, and compatibility rules.
• Package schemas in the distribution and publish them from the documentation site.
• Add generated or reference validators and schema-version tests.

Acceptance criteria

• Each documented machine contract has a versioned schema artifact.
• Schemas validate all supported examples and reject malformed payloads.
• Schema changes are covered by compatibility tests and release notes.
• Consumers can use the artifacts from another language or process.

Project fields

• Status: Backlog
• Priority: P1
• Area: Python
• Initiative: v1.0 Readiness
• Size: M