docs: clarify compiler and runtime positioning

[abrichr]

Summary

• explain the compiler and governed runtime in direct, buyer-focused language
• remove the static Beta and Available maturity labels from the flagship Flow README
• derive current product state from the central signed release-admission record
• keep product release admission separate from exact workflow qualification
• preserve the browser attach resize and multi-monitor contract without claiming unfinished cross-surface geometry work

Validation

• python scripts/check_consistency.py: passed
• pytest tests/test_consistency.py tests/test_validate_claims.py: 47 passed
• exact-head GitHub checks: all completed checks pass; the full test job is still running
• git diff --check: passed

Merge condition

Keep this PR in draft until every exact-head check passes, an independent reviewer approves the final diff, and the public lifecycle endpoint consumes the exact v2 activation and revocation contract.