feat(sync): apply legacy shared review reassignment

[kunickiaj]

Description

Adds the explicit apply step for legacy-shared-review groups so reviewed historical rows can be reassigned to a selected Sharing domain without automatic promotion.

The flow previews counts first, requires explicit old-copies confirmation, enforces local device membership for the target domain, rejects local-default/legacy targets, skips peer-owned rows, and keeps the old-copies warning visible.

Type of Change

• 🚀 Feature (new functionality)
• 🐛 Bug fix (fixes an issue)
• 📚 Documentation (docs-only change)
• 🔧 Maintenance (refactor, chore, CI, etc.)
• 🧪 Testing (test-only changes)

Testing

• Relevant checks pass locally (pnpm run tsc, pnpm run lint, pnpm run test)
• Added/updated tests for changes
• Manually verified changes work as expected

Targeted/local checks run:

• pnpm exec vitest run packages/viewer-server/src/index.test.ts --testNamePattern "legacy shared review" packages/ui/src/tabs/sync/components/sync-sharing-review.test.tsx
• pnpm run tsc
• pnpm run lint (passes with existing FeedItemCard info warnings)
• pnpm --filter @codemem/ui build
• git diff --check

Checklist

• Code follows project style (pnpm run lint passes for touched files)
• Self-review completed
• Documentation updated (if needed)
• No new warnings introduced

[kunickiaj]

• feat(sync): apply legacy shared review reassignment #1088 👈 (View in Graphite)
• main

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[kunickiaj]

Merge activity

• May 12, 11:05 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 12, 11:05 PM UTC: @kunickiaj merged this pull request with Graphite.