Fix anatomy quiz system selection and add i18n + tests

[ianfhunter]

Motivation

• The quiz was only selecting new targets from the currently visible system, causing repeated items when viewing a different system; the UI also contained hardcoded English strings that should use i18n.

Description

• Decoupled question selection from the visible system by selecting from ALL_PARTS while rendering only the systems that should be visible; added getDisplaySystemIds to compute which systems to show when a target belongs to a different system (src/pages/AnatomyQuiz/anatomyQuizUtils.js).
• Updated AnatomyQuiz.jsx to use the new display logic and displayParts for the SVG, and to keep selection deterministic via the existing seeded RNG (src/pages/AnatomyQuiz/AnatomyQuiz.jsx).
• Replaced several hardcoded UI strings with t(...) calls to enable i18n (hints, messages, labels, buttons).
• Added unit tests for the new display-system logic and imported the utility into the existing test suite (src/pages/AnatomyQuiz/AnatomyQuiz.test.js).

Testing

• Ran the Anatomy Quiz unit tests with Vitest: npm run test:run -- src/pages/AnatomyQuiz/AnatomyQuiz.test.js, and all tests passed (19 tests, 1 file).
• No other automated test failures were observed for the modified files.

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