feat: add transform for useMergerefs

[adrienzheng-cb]

What changed? Why?

Summary

This PR extends the CDS migrator for the v8 → v9 workflow: a new useMergeRefs → mergeRefs codemod, button-variant-values moved under transforms/v9/ with scope-agnostic import matching, and an optional npm package scope flag so consumers can limit rewrites without hard-coding internal registry names.

What changed

New: migrate-use-merge-refs (v9)

• Rewrites deprecated useMergeRefs imports from @<scope>/cds-common/hooks/useMergeRefs to mergeRefs from @<scope>/cds-common/utils/mergeRefs (scope is preserved).
• Handles imports, re-exports, aliases, Jest mocks, duplicate import consolidation, and safe identifier renames (skips object keys, member access, etc.).
• Scope matching: recognizes @<any-scope>/cds-common/... so the open-source migrator does not depend on a specific org prefix.
• Registered in the v8-to-v9 preset manifest; includes fixtures and Jest coverage.

button-variant-values (v9)

• Lives under packages/migrator/src/transforms/v9/.
• Import detection uses @<scope>/cds-web and @<scope>/cds-mobile (any scope), not a fixed list of scoped package names.

CLI: package scope (-ps / --package-scope)

• --package-scope <scope> (shorthand -ps) limits scope-aware transforms to a single npm scope (e.g. coinbase or @coinbase).
• Omitted → all scopes matching the transform rules are rewritten.
• The runner forwards --packageScope=… to jscodeshift; transforms read options.packageScope.
• packages/migrator/src/utils/package-scope.ts centralizes normalization (coinbase → @coinbase) and reading options.

Docs & tooling

• CLI_REFERENCE.md updated for package scope and shorthand.
• Test helpers / Jest config / fixture layout aligned with the new v9 transforms.

Usage examples

# Preset (includes new transform when selected in manifest)
npx @coinbase/cds-migrator ./src -p v8-to-v9

# Direct transform
npx @coinbase/cds-migrator ./src -t migrate-use-merge-refs

# Only @coinbase/* CDS imports
npx @coinbase/cds-migrator ./src -t button-variant-values -ps coinbase

Root cause (required for bugfixes)

UI changes

iOS Old	iOS New
old screenshot	new screenshot

Android Old	Android New
old screenshot	new screenshot

Web Old	Web New
old screenshot	new screenshot

Testing

How has it been tested?

• Unit tests
• Interaction tests
• Pseudo State tests
• Manual - Web
• Manual - Android (Emulator / Device)
• Manual - iOS (Emulator / Device)

Testing instructions

Illustrations/Icons Checklist

Required if this PR changes files under packages/illustrations/** or packages/icons/**

• verified visreg changes with Terran (include link to visreg run/approval)
• all illustration/icons names have been reviewed by Dom and/or Terran

Change management

type=routine
risk=low
impact=sev5

automerge=false