fix: guard wallet storage against QuotaExceededError and SecurityError

[Kaycee276]

Guard wallet.ts's localStorage calls against SecurityError/QuotaExceededError

Context

Browsers can throw synchronously from localStorage.getItem/setItem in restricted contexts (e.g., Safari private browsing throwing a QuotaExceededError, or embedded contexts throwing a SecurityError). Because WalletProvider called these synchronous methods directly without a try/catch, it caused uncaught exceptions, entirely breaking the "Connect wallet" button and mount restore effect in those environments rather than failing gracefully.

Implementation Details

• Wrapped all window.localStorage.getItem, setItem, and removeItem calls in src/lib/wallet.ts within try/catch blocks.
• On caught errors, loadAccount returns null safely.
• saveAccount and clearAccount fail silently without propagating the exception.
• Addressed SEED_STORAGE_KEY generation gracefully handling storage failures.
• Added test suites simulating SecurityError and QuotaExceededError around Storage.prototype overrides inside src/lib/wallet.test.ts.
• Implemented mocked error assertions in src/components/WalletProvider.test.tsx to verify that WalletProvider updates in-memory UI connection state cleanly despite the underlying local persistence failing.
• Added SSR tests validating code fallback execution where window is undefined.

Verification

• Validated all tests passing locally for the wallet flow context (npm test -- src/lib/wallet.test.ts src/components/WalletProvider.test.tsx).
• Ensured 100% test branch and line coverage thresholds for src/lib/wallet.ts and src/components/WalletProvider.tsx are met.

closes #241