chore: prepare extension integration RCs

[developer-1px]

Summary

• prepare grouping, patch-preview, and search-replace as 0.1.1-rc.0 companion prereleases
• accept the stable 1.0.1+ core line and 1.1.0-rc.* integration line without moving latest
• add exact-pin integration documentation and package-local MIT licenses
• extend the protected publish workflow with an aggregate extension RC tag
• lock grouping selection changes into the same commit/history boundary and cover undo/redo selection restoration

Verification

• targeted verify for all three RC packages
• full npm run extensions:verify
• docs generation/check and lockfile dry-run
• npm strict clean graph smoke with core 1.1.0-rc.0 and all three extension tarballs
• stable core 1.0.1 peer-resolution smoke for grouping
• tarballs contain only package metadata, README, LICENSE, JS, and declarations
• workflow YAML and extension tag identity guard validated locally

Release

After merge, configure Trusted Publisher entries for the three packages and add the protected tag policy, then tag the merged commit as json-document-extensions-v0.1.1-rc.0. The workflow publishes each package only under next with provenance.