Fix unintended Windows key switching

[onderaktas54]

What changed

• parses single-character hotkey tokens before enum parsing, so 1 and 2 map to keyboard VK codes instead of mouse button codes
• releases Host-side Ctrl, Alt, Shift and both Windows keys whenever routing mode changes
• marks those synthetic releases so they are never forwarded to the Client
• registers global hotkeys with MOD_NOREPEAT to prevent held shortcuts from retriggering
• adds Windows regression tests for Ctrl+Win+1, Ctrl+Alt+2, and Shift+A

Root cause

.NET Enum.TryParse accepts numeric strings as raw enum values. The old parser therefore interpreted 1 as VK_LBUTTON and 2 as VK_RBUTTON, rather than keyboard VK_1 and VK_2. A mode-switch modifier could also remain logically held on the Windows Host because its physical key-up was blocked after entering remote mode. Together, holding Win and clicking could match the malformed return-to-Host hotkey and switch routing unexpectedly.

Validation

• Windows Host Release build: succeeded, 0 warnings
• Windows hotkey test project: builds successfully on Linux with Windows targeting
• Core tests: 20 passed
• Linux tests: 8 passed
• Windows regression tests are now part of the Windows CI job