loadState() took hasWallet straight from storage, so any profile persisted
with the flag out of step with wallets stayed broken on every subsequent
load rather than only until the next write. The flag is now derived from
wallets.length at load time.
The only consumer is the popup's welcome-vs-wallet-list gate in
src/popup/index.js; the only writers set it true alongside an added
wallet. Nothing reads it expecting it to differ from wallets.length, so
deriving is safe and needs no write-back on load.
