Document daily public validation cadence

[Brandon Miller (brandom-msft)]

Summary

• expose the daily public validation cadence from the root README
• document deterministic inventory discovery, invalid-YAML quarantine, duplicate-ID rejection, and the verified 74 visible / 55 eligible / 19 skipped snapshot (12 invalid YAML and 7 unsupported Rust)
• record the two eligible samples that declare Live-service validation
• 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 32821260320: 77/77 jobs succeeded and 76 artifacts published (74 per-sample, manifest, and consolidated run artifact)

Tracking

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

[Brandon Miller (brandom-msft)]

Superseded by #944, a clean replacement based on current main that consolidates the contributor and validation guidance.