Add instant image translation (Google Lens style)

[quangdat99x]

Summary

Adds a new Alt+D hotkey that turns a screen selection into a Google Lens style translation: OCR the region, auto-detect the source language, translate, and paint the translation over the original text positions in a floating overlay. A small toolbar offers source-override + target-language dropdowns (live re-translate), copy-all, and Esc/click-away to close. Default target is Vietnamese.

What''s inside

• Positional Windows OCR + auto-detect — Translumo.OCR/WindowsOCR/WindowsOcrPositional.cs: keeps per-line bounding boxes and detects the source language by running the installed recognizer packs and scoring each result by how many characters match that language''s writing system (the UWP OCR API exposes no per-word confidence, so a script-match heuristic is used).
• Auto-source translation — AutoSourceGoogleTranslator sends sl=auto, reusing the proxy-aware GoogleContainer and result regex without disturbing the config-bound GoogleTranslator used by continuous translation.
• Orchestration — ImageTranslationService runs OCR then per-line translation with bounded concurrency.
• Overlay — ImageTranslationOverlayWindow shows the frozen region snapshot with translated boxes at the original positions and the toolbar; changing a dropdown re-runs the pipeline and repaints.
• Wiring — new ImageTranslateKey (default Alt+D) across HotKeysConfiguration / HotKeysServiceManager, a configurable row in Hotkeys settings, ChatWindowViewModel handler (region capture + overlay), DI registration, and localization strings (en/ru/zh).

Notes / limitations

• Source auto-detect for the OCR step depends on which Windows OCR language packs are installed (Windows OCR has no native auto recognizer); the inline source dropdown lets the user override. The translation step always uses sl=auto.
• Line-by-line translation preserves layout but loses cross-line context (same trade-off as Lens).

Test plan

• dotnet build Translumo.sln -c Release — 0 errors.
• Ran the app, pressed Alt+D, selected a region of English text: overlay auto-detected en-US, translated to Vietnamese over the original lines, and switching the target dropdown to Spanish live re-translated all lines. Copy and Esc work.

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