Remove Electron app source

[enaboapps]

Summary

• remove the old Electron/TypeScript app source and config
• remove Electron-only native helper sources and smoke scripts
• keep temporary npm wrappers only for C# package staging until the npm removal issue
• trim CI so this branch validates the C# app path

Closes #281.

Validation

• dotnet restore src-dotnet/SwitchifyPc.sln
• dotnet build src-dotnet/SwitchifyPc.sln -c Release --no-restore
• dotnet test src-dotnet/SwitchifyPc.sln -c Release --no-build
• npm ci
• npm run dotnet:package:win:stage
• npm run dotnet:package:win:verify
• rg -n electron-builder|electron-vite|@nut-tree|react|vite|vitest|src/main|src/renderer|src/shared . -g !package-lock.json -g !dist* -g !src-dotnet/**/bin/** -g !src-dotnet/**/obj/**