Document daily public validation cadence

[Brandon Miller (brandom-msft)]

Summary

• expose the daily public validation cadence from the root README
• document deterministic inventory discovery, malformed-metadata quarantine, duplicate-ID rejection, and the verified 53 executable / 19 skipped snapshot
• add a language-by-language build-readiness matrix, including declared-command precedence and unsupported Rust behavior
• document schema-v2 production, schema-v1 reader compatibility, outcomes, artifacts, and action-first same-run reporting
• preserve the legacy L4-validation environment name only as an external infrastructure identifier
• identify the remaining live-service onboarding, cold-provisioning, quarantine-automation, and Rust-readiness scope without presenting P4 as complete

Validation

• producer and reporting contract suites (18 tests)
• tox -e typos for all changed Markdown files
• local documentation link checks
• language matrix consistency against validator routes and declared-command precedence
• live schema, inventory, terminology, schedule, concurrency, artifact, provisioning-policy, discovery, and report consistency checks
• authoritative run 31649334462: 75/75 jobs succeeded and 74 artifacts published

Tracking

ADO 5510709 — https://msdata.visualstudio.com/Vienna/_workitems/edit/5510709