feat: implement PWA offline mode with IndexedDB queue and sync manager

[SaumyaSngh323]

Description

Checklist

• npm run lint passes with no errors
• npm run build compiles without TypeScript errors
• python -m pytest passes (including new tests I added)
• No .env files, API keys, secrets, model weights, or __pycache__ in this diff
• Branch is rebased on main, not merged

Closes #6

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Project	Deployment	Actions	Updated (UTC)
fresh-scan-ai	Ready	Preview, Comment	Jun 6, 2026 9:44am

[jpdevhub]

Thier are many error in the code first git pull as many backend new code are been added due to the onnx update then fix some listed issue then i will review the code:
Service Worker Crash: Overwrote vite.config.ts, completely removing the globIgnores fix we added recently! If merged, the app will try to precache the 26MB .wasm file again and crash.
Fake API Endpoint: Used an API endpoint (/api/scans) that doesn't exist on your backend.
Invalid Data Format: They are trying to use JSON.stringify() to send images, but your backend requires multipart/form-data for file uploads.
Disconnected Code: The queue isn't actually wired up to the ScannerPage.tsx interface.