Update documentation to reflect the merged main implementation #9

PR #2 is merged into new-development and PR #3 is merged into main at 2893b6c. Current status/handover/development guidance still includes draft-PR and pre-merge statements.

• Update current branch/merge/status guidance without erasing historical baseline evidence.
• Link merged-main CI evidence and identify remaining manual/owner gates.
• Update clean-checkout instructions, roadmap and unreleased changelog as needed.
• Keep registry installation guidance honest until publication is verified.

Acceptance: no current-status claim that the merged implementation is still a draft or unmerged; docs match actual release state.

References: roadmap, development/acceptance guide.