Fix Windows window sizing at high display scaling

[Functionhx]

At 150% display scaling on a 1920×1080 Windows 11 desktop, the 1.9.2 main window opens above the screen and hides the exam tabs. The OCR review dialog also places its confirmation controls below the visible work area. Both problems were reproduced with the published ZIP in a clean KVM guest.

Size the main window and OCR review dialog against the WPF desktop work area, leaving a small margin. Clamp the main window's minimum dimensions to the available area, and give the exam tab buttons explicit accessibility names.

Validation:

• Windows, macOS and Android CI passed on this commit.
• Tested the CI Windows artifact in the same Windows 11 guest at actual 144 DPI (150%). The main window changed from (-30, -149, 1946, 1106) to (12, 12, 1896, 984) and the OCR dialog is (173, 12, 1575, 984), both fully within the desktop work area.
• Verified all three named exam buttons are physically visible. The native picture picker, real OCR, mandatory review checkbox, editable recognition text and confirmed question import passed. The candidate's existing self-tests, including real OCR, passed in the VM.
• The original release also passed clean launch without installing .NET, bundled 33 writing and 33 translation questions, native Tab/undo/alignment, paused submission timer, encrypted key persistence and full Windows restart recovery.

The VM confirmed that OCR needs the documented Visual C++ x64 runtime: it failed before installation and passed afterward. This PR does not change that prerequisite.