feat(native): C# input/capture sidecar replacing the PowerShell helper

Implements ADR-008. native/input-helper is a self-contained .NET 9 console exe
speaking the identical JSON-over-stdin/stdout protocol as the old PowerShell
helper (ping/cursor/runtime/focus/click/scroll/bounds/capture), so the
InputHelperService interface is unchanged.

- Win32 interop compiled once (native exe), not per call.
- PerMonitorV2 DPI via manifest so click/capture coordinates stay correct on
  mixed-DPI multi-monitor setups.
- capture returns base64 PNG bytes inline (imageBase64) instead of writing a
  temp file per frame; the client handles both base64 and the PowerShell path.
- InputHelperClient prefers the exe and falls back to the embedded PowerShell
  helper when the exe is absent, so the app still runs without the .NET build.
- main.ts resolves the exe (INPUT_HELPER_EXE env -> packaged resources/input-helper
  -> native/input-helper/bin/publish). electron-builder ships it via extraResources.
- npm run helper:build; README documents the build + fallback.

Verified end-to-end through the compiled client: sidecar spawns, runtime info
and a base64 primary-screen capture return correctly. Build stays green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -34,6 +34,20 @@ npm run dev
 
 Use the Electron app window for scanner work. The browser preview does not expose the local capture bridge.
 
+### Input/Capture helper (C# sidecar)
+
+Input automation and screen capture run through a compiled C# sidecar
+(`native/input-helper`, see ADR-008). Build it once:
+
+```powershell
+npm run helper:build   # requires the .NET SDK; produces a self-contained exe
+```
+
+The app auto-detects the exe (`INPUT_HELPER_EXE` env override → packaged
+`resources/input-helper` → `native/input-helper/bin/publish`). If the exe is not
+present it falls back to the embedded PowerShell helper, so the app still runs
+without the .NET build - just slower and with the old per-frame temp-file capture.
+
 ### Automatischer Scan: als Administrator starten
 
 Genshin läuft erhöht (Administrator). Windows (UIPI) verwirft dann alle simulierten Maus-Eingaben aus einer nicht-erhöhten App - SendInput meldet dabei trotzdem Erfolg. Für den automatischen Scan muss die App deshalb ebenfalls erhöht laufen: