Complete the v2 stable gate

[developer-1px]

Summary

• converge Core equality and canonical array-index primitives, with cross-package parity vectors
• add a reference-free six-member implementation and five pressure verticals across reference, independent, and collaboration bindings
• declare the Projection Profile Stable and prepare Core 2.0.0 plus companion rc.1 releases

Verification

• npm run release:check
• npm run verify, with the repaired public-doc boundary followed by site tests, Pages verification, and browser tests
• Core: 220 passed, 2 skipped; collaboration: 112 passed; contenteditable collaboration: 17 passed

Closes #218