Add exam translation practice and native Windows/Android apps

[Functionhx]

Changes

WriteBench now includes eight exam tasks: Kaoyan English I small/large essays and translation, English II translation, CET-6 writing/translation, and IELTS Academic Tasks 1/2. English-to-Chinese answers use Chinese corrections and independent 10/15-point rubrics; no English-word minimum blocks submission.

Adds native Windows WPF and Android Studio projects with real local OCR confirmation, three independent DeepSeek/MAX reviews, local median/spread aggregation, persistence, review and rewrite. Desktop judges can independently use official Codex CLI/MAX; Android uses DeepSeek directly. Exam category icons and concise task tabs preserve the quiet UI; phone Start remains pinned above navigation.

Fixes an observed macOS submission hang caused by reading a legacy Keychain item on the main thread. Submission now reads memory only; optional secure persistence/restoration runs in the background and never reads old development credentials. Missing Key displays an immediate prompt and no simulated score.

Validation

• macOS: 29 tests passed; actual English II immersion and immediate missing-Key alert checked.
• Windows 11 x64: self-contained build, executable domain/JSON/persistence checks and real Tesseract OCR passed; actual WPF view rendered for inspection.
• Android: five JUnit tests plus two actual-device service tests (local OCR and Chinese rewrite persistence), release build, APK signature verification and installation passed; launched through the user's Android Studio on Android 15 ARM64.
• Adds CI for all three native builds. Final visual checks, release packaging and checksum verification are recorded in Documentation/Validation.md.
• No API keys, Codex credentials, user histories or signing keys are committed. Live paid mixed grading and Windows Codex login are not claimed as verified.

Windows and Android are explicitly labeled 0.1 preview builds. macOS is 1.3.0. README documents provider/platform differences and signing status.

Closes #1