Deleting a wallet left three defects in the same path:
- `hasWallet` stayed true after the last wallet was deleted, so the next
popup open rendered Home with "No wallets yet" instead of Welcome. It
now tracks whether any wallet remains.
- The selection was reset to wallet 0 / address 0 unconditionally.
`selectedWallet` now follows the splice (decremented when a wallet
before it is removed), and only falls back to the first remaining
wallet's first address when the selection itself was deleted;
`activeAddress` only moves when it belonged to the deleted wallet.
- No `AUTISTMASK_ACTIVE_CHANGED` was sent, so connected sites kept
reporting a deleted address. The delete path now broadcasts it after
the state is persisted, whenever the active address actually changed,
and the background re-emits `accountsChanged` from there.
The transition moved into `src/shared/walletDelete.js` so it can be
tested without a DOM. Site-permission cleanup is unchanged and still
covers every address of an HD wallet.
