feat: Epic #133 Japanese Workspace Enhancement

[Dyu20705]

Resolves #133, Resolves #134, Resolves #135, Resolves #136, Resolves #137, Resolves #138.

This PR implements the Japanese Workspace Enhancement epic.

Architectural Decisions & Module Mapping

The original spec proposed creating several new UI components (ui/japaneseReviewModal.js, ui/flashcardView.js, ui/japaneseDashboardView.js). However, per AGENTS.md ("Do not create duplicate owners for... review state, drawing state, or persistence"), I elected to integrate these directly into their existing canonical owners to avoid duplication:

• Gamification ([Japanese][1/5] Implement Gamification Engine (Streaks, XP, and Achievements) #134): Implemented in core/gamificationEngine.js and stored atomically in STORE_SETTINGS via core/japaneseV2Storage.js (satisfying core/storage.js requirement).
• Daily Goals ([Japanese][5/5] Implement Daily Study Goal Setting and Progress Tracker #138): Implemented in core/dailyGoals.js and stored alongside Gamification. UI integrated directly into the existing renderDashboard in ui/japaneseApp.js.
• Fluid Flashcard ([Japanese][2/5] Implement Fluid Flashcard Review UI with Animated Flip and Rating Feedback #135): Integrated into ui/japaneseApp.js and styles/japanese.css using display: grid and 3D transforms.
• Kanji Canvas ([Japanese][3/5] Enhance Kanji Vector Drawing Canvas with Stroke History, Order Guide, and PNG Export #136): Directly enhanced the existing ui/kanjiInkView.js to support Replay, high-res PNG export, and the Guidance placeholder.
• Quick Study ([Japanese][4/5] Implement Quick Study Sessions with Configurable Time-Boxed Batches #137): Managed through core/japaneseState.js and core/japaneseActions.js by adding a configurable limit rather than creating a duplicate state owner. UI buttons were appended to ui/japaneseApp.js.

Verification Evidence

All automated gates pass successfully:

npm run lint          # PASS
npm run test:unit     # PASS
npm run test:integration # PASS
npm run test:e2e      # PASS (138 passed)

Acceptance Criteria Mapping

• Gamification: XP and streak calculated deterministically.
• Fluid Review: 3D flip animation, <kbd>Space</kbd> to flip, <kbd>1-4</kbd> to rate.
• Kanji Tools: 4096 points limit maintained, transparent PNG export command (export.kanji-png), history traversal via Replay button.
• Quick Study: Configurable limits (5, 10, 15) correctly filter the review queue.
• Daily Goals: Target tracking integrated without modifying the core Anki/SM2 scheduler logic.

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