Wire Folder Compare Next Difference and disable leftover unused verbs

[baseGame]

Summary

Search Next/Previous Difference was enabled on Folder Compare but fell through to Select All. The same verbs were enabled on Folder Sync and Merge, where they only opened filters. Registry Session Rules/Settings and folder Actions were enabled with no handler.

This change:

• Steps Folder Compare Next/Previous Difference from the existing row navigator.
• Disables Next/Previous Difference on Folder Sync and Merge (Next/Previous Conflict stays).
• Disables Registry Session Rules/Settings and unused folder Actions; Expand/Collapse stay enabled.

Compare/Merge/Sync Base Folders still open an empty session. Text Merge four-pane and live Registry hive are still out of scope.

Type of change

• Bug fix
• New feature
• Documentation
• Refactor
• Build, CI, or release

Validation

• corepack pnpm format:check
• corepack pnpm lint
• corepack pnpm stylelint
• corepack pnpm typecheck
• corepack pnpm exec vitest run src/views/FolderCompareView.test.ts src/app/menuTables.test.ts src/layouts/AppLayout.test.ts

Local Rust clippy needs a newer Cargo than this host; Windows Quality CI covers that.

Checklist

• I kept the change focused.
• I added or updated tests where needed.
• I updated documentation for user-facing changes.
• I checked that no sensitive data is included.