docs: clarify secret key handling and SDK responsibility in wallet re…

[Damola-Sodiq]

docs: clarify wallet recovery limitations and SDK handoff boundaries

Summary

Clearly documents wallet recovery limitations, key loss scenarios, unsupported recovery capabilities, and consumer safe-storage responsibilities to ensure honest wallet security communication for SDK integrators.

Key Changes

• Local Wallet Generation & Import Boundary: Added explicit code examples and documentation in docs/wallet-recovery-limitations.md covering createWallet() and importWallet().
• Handoff Boundary: Clearly defines that the SDK handles keypairs statelessly in memory; persisting keys into secure storage or initiating user backup flows is strictly the consuming application's responsibility.
• Explicit Limitations & Non-Capabilities: Outlined that the SDK deliberately does not provide key escrow, password-based resets, social recovery, cloud sync, or automated multi-sig.
• Platform Integration Guidance: Included platform-specific advice for:
  • Mobile: iOS Keychain, Android Keystore, React Native (Expo SecureStore, react-native-keychain).
  • Web: Web Crypto API (non-extractable keys), IndexedDB, and security warnings against localStorage.
• README Cross-Linking: Verified linkages in README.md within the documentation index and security CAUTION block.

Acceptance Criteria

• Recovery limitations documented
• Consumer vs SDK responsibilities defined
• Overpromising avoided (stateless, non-custodial model enforced)
• Mobile and web integration notes included
• README links to document

Verification

Executed npm run verify:

• tsc --noEmit (0 linter errors)
• check-circular-deps (Clean across 27 modules)
• vitest run (567 passed, 1 skipped across 28 test suites)
• tsc (Production build succeeded)

closes #180