fix(dashboard): don't expose wallet address in expiry-notified storage key (#548)

[boluwacodes]

Summary

DashboardPage stored the IDs of policies it had already warned about under the sessionStorage key ps_expiry_notified_${address}. Anyone looking at DevTools → Application → Session Storage could read the raw Stellar wallet address in the key name.

Changes

Commit 1: fix

• New src/lib/storageKeys.ts
  • fingerprint(value): a small, deterministic, non-reversible 53-bit hash (cyrb53) that returns a short base-36 string. It is synchronous, so it works inside the existing effect without an async crypto.subtle call.
  • expiryNotifiedStorageKey(address): returns ps_expiry_notified_<fingerprint>.
• src/app/dashboard/page.tsx: the effect builds its key with expiryNotifiedStorageKey(address). Nothing else in the effect changes.

Commit 2: tests (src/__tests__/storageKeys.test.ts)

• The key never contains the full wallet address or its first 8 characters.
• It is the same for the same wallet, so the "already notified" record still works.
• It is different for different wallets.

Notes

• Existing sessions: a key written under the old format is simply not found any more. At worst a user sees an expiring-policy warning one more time in their current tab. sessionStorage is cleared when the tab closes, so no migration is needed.
• Why a non-cryptographic hash: the aim, as the issue says, is to keep the address from being readable in key names. Anyone who already knows an address could hash it themselves with any deterministic hash, crypto or not, so a slower cryptographic hash would add nothing here.
• Overlap with PR fix(dashboard): show expiry warning toast once per policy (#532) #630 ([bug] Dashboard expiry warning fires duplicate toasts across re-renders #532): that PR moves this effect into a useExpiryWarnings hook. The two changes touch the same one line. Whichever merges second only needs expiryNotifiedStorageKey(address) in place of the template string.

Testing

npx vitest run src/__tests__/storageKeys.test.ts
 Tests  3 passed (3)

tsc --noEmit reports no errors in the changed or new files.
Closes #548
Closes #549
Closes #550
Closes #551

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