Execute the v2.0 release-candidate to GA checklist

## Parent

- #2

## What to build

Run the complete v2 release checklist against candidate artifacts, including clean-room installation, v1 upgrade and migration checks, documentation publication, rollback readiness, and post-release smoke verification.

## Acceptance criteria

- [ ] Candidate wheels and source distribution pass clean-room installation on the supported matrix.
- [ ] Documented v1 upgrade and v2 migration paths are exercised against released artifacts.
- [ ] PyPI, CLI, SDK, and documentation smoke checks pass from public endpoints.
- [ ] No P0 or P1 issue remains open when GA is published.
- [ ] Rollback, yank, and one-week observation ownership are recorded.

## Blocked by

- #20
- #25
- #30
- #34
- #29
- #28

## RFC-0005 contract

Execute the RFC-0005 M5 mapping for `v2.0.0` and verify every cumulative evidence record, public endpoint, artifact digest, milestone link, observation owner, and rollback owner. A green build alone is not GA completion.

Start with the RFC-0005 M5 mapping and review blocked issues #20, #25, #30, #34, #29, and #28. Run the complete checklist against candidate artifacts, including clean-room installation, migration, public endpoint smoke checks, rollback readiness, and observation ownership. Done means every evidence record and acceptance criterion is verified before v2.0.0 GA.

Written by the indexing model from the issue text.