Improve card management, import flow, and mobile review UX

[sergeyampo]

Summary

This PR tightens several rough edges across deck management, note browsing, importing, and the mobile learning flow.

What changed

• renamed the deck Notebook area to Cards and moved the related UI into the new src/app/cards module
• made card/note previews show both front and back across the deck cards list, Manage Cards table, and Spotlight results
• unified note search so Manage Cards, Spotlight, and deck card filtering all search across front and back content, including Cyrillic text
• implemented CrowdAnki JSON import support, including field mapping, bulk note creation, and test coverage
• optimized large imports by batching note/card writes instead of creating each entry one-by-one
• fixed new card creation issues around deck selection persistence and add-card completion flow
• updated note editor typography so non-Latin text renders with a broader fallback font stack
• fixed mobile layout issues for the new-card screen and the finished-learning screen after all cards are reviewed
• updated local run instructions and Tauri commands in the README/config so the app runs through pnpm

Why

The repo had a cluster of UX and workflow gaps that made the app feel unreliable in a few high-traffic paths:

• imported decks could fail or feel excessively slow
• note discovery surfaces only showed the front side even when the back side was the useful context
• the old Notebook naming no longer matched the actual product concept
• mobile completion states could render incorrectly and hide the final session summary
• non-Latin text previews were not consistently legible

Validation

• corepack pnpm test
• corepack pnpm run lint:type
• corepack pnpm run lint
• corepack pnpm run build

Notes

The lint run still reports the existing warning-only accessibility/security/performance findings already present in the repo; this PR does not introduce new lint errors.

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