Split shared reviewer TypeScript plumbing

[andrewsanchez]

Source split from ankitects#4289.

Breakdown sections covered:

• 19. Undo / redo integration
• 29. Keyboard shortcuts
• 31. Night mode / theme consolidation

Source fidelity:

• This PR copies exact final file contents from PR Feat/Svelte port for reviewer ankitects/anki#4289.
• No implementation changes were made while splitting.
• Commit author is preserved as Luc Mcgrady.

Follow-up notes from the breakdown:

• The .which to .key / .code shortcut change may need follow-up for non-Latin keyboard layouts.
• Undo/menu-label synchronization depends on the operation-event plumbing and still needs review.