Split reviewer answer count and timer UI

[andrewsanchez]

Source split from ankitects#4289.

Breakdown sections covered:

• 9. Answer buttons moved into reviewer page
• 10. Answer timing and millisecondsTaken
• 11. Remaining counts display
• 12. Card answer timer
• 26. Auto Advance UI/timer wiring
• 27. Congratulations/empty-queue path support from the UI side

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 old bottom webview is hidden rather than eliminated, so performance benefit is not fully realized yet.
• Auto Advance "wait for audio" remains unfinished.
• A processing placeholder and leech tooltip remain open items.