- Add src/lib/sessionCrypto.ts with AES-GCM-256 non-exportable session keys
- Integrate into Backup flow: auto-clear plaintext mnemonic after QR generation
- Add Lock/Clear button to destroy session key and clear all state
- Add cleanup useEffect on component unmount
- Add comprehensive GEMINI.md for AI agent onboarding
- Fix TypeScript strict mode errors and unused imports
Tested:
- Session-key encryption working (mnemonic clears after QR gen)
- Lock/Clear functionality verified
- No plaintext secrets in localStorage/sessionStorage
- Production build successful
