docs: record v2 RC consumer and rollback evidence

[codeforester]

Summary

• record the immutable v2.0.0-rc.1 reference and verified asset set
• record merged Base and Base Demo RC pins plus hosted validation evidence
• record the Homebrew RC formula rehearsal, v2 API expectations, and stable rollback
• advance the machine-readable consumer states without claiming GA

Issue

Related to #240

Validation

• `git diff --check`
• `scripts/first-party-cutover check --allow-pending --base-dir /Users/rameshhp/work/base --base-demo-dir /Users/rameshhp/work/base-demo`
• `bats tests/vendor.bats`
• `bats tests/reference-apps.bats`
• `./tests/validate.sh` (the first run was intentionally rejected by the clean-checkout release-artifact guard before commit; the individual BATS suites and cutover checks passed)

Docs Impact

The readiness ledger now distinguishes immutable RC evidence from GA support
and records that the eventual v2 Homebrew formula must consume the bundle
layout and `base_` API. Stable Homebrew remains v1.4.0 until GA.