build: migrate simulator to browser Vite SPA

[prashant2007-wq]

Summary

Closes #150.

Migrates ns-simulator from an Electron app shell to a browser-hosted Vite SPA.

Changes

• Replaced electron.vite.config.ts with a standard vite.config.ts.
• Configured Vite to use src/renderer as the browser app root.
• Updated npm scripts to use vite, vite build, and vite preview.
• Removed Electron packaging/start scripts and dependencies.
• Replaced Electron IPC file save/load with browser-native file APIs.
• Added File System Access API support for Chromium.
• Added fallback open flow using hidden file input.
• Added fallback save flow using Blob download.
• Replaced Electron discard confirmation with browser confirmation.
• Replaced Electron close interception with beforeunload.
• Removed src/main, src/preload, IPC handlers, Electron builder config, and app update config.
• Updated TypeScript config for browser-first build.
• Kept the CLI entrypoint available through npm run simulate.

Testing

Ran:

npm run typecheck
npm run test
npm run build
npm run lint

Manual browser verification:

• Opened app through Vite dev server.
• Confirmed .json scenario opening works.
• Confirmed .json scenario saving works.
• Confirmed Cmd/Ctrl+O opens file picker.
• Confirmed Cmd/Ctrl+S saves the current scenario.
• Confirmed opening a file with unsaved changes asks for confirmation.
• Confirmed reloading/closing the tab with unsaved changes triggers the browser leave prompt.
• Confirmed production build outputs static assets into dist/.

Notes

Safari and Firefox do not support Chromium’s File System Access API, so they use the fallback download/input flows and may re-prompt during save, as expected in the issue scope.

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