[Positioning] Document public-preview → GA criteria

[khelanmodi]

Goal

Explicit list of what needs to be true before GA. The reviewer (item #10) implicitly wants this.

What to ship

A "Path to GA" summary at the top of docs/release-readiness-check.md listing:

• Items currently done.
• Items still required before GA.
• Items deferred past GA (and the reason).

Categories:

• Security (RBAC sections 3, 4, 4a — track per current checklist).
• DX (Tier 1 issues in this project).
• Telemetry (driver appName + future server-side).
• Positioning artifacts (statement, comparison, audiences, roadmap).
• Hosted runtime (if applicable per Positioning Q2).

Acceptance criteria

• Top-of-document summary table, not buried.
• Each item links to the issue / PR that tracks it.
• Reviewed by PM before each release.

Depends on

• Positioning Q2 (hosted-runtime decision) affects this list.