feat: remove an address from an HD wallet, behind a confirmation (closes #162)

Address rows on Home now carry an [x] control on wallets that derive their
addresses from an extended key and hold more than one; it opens a
confirmation screen before anything is removed.

Removing an address destroys nothing, and the copy says so: the address stays
derivable from key material the wallet still holds, any funds at it stay
where they are, and importing the recovery phrase brings it back. That is
also why the screen is not password-gated, unlike delete-wallet — a password
gates the disclosure or destruction of a secret, and this does neither. A
balance is surfaced as a warning line, never as a refusal.

The state transition lives next to the wallet one in
src/shared/walletDelete.js and shares its address comparison, site-permission
cleanup and broadcast, so the rules match one level down: the last address of
a wallet is never removable, the selection moves only when it was the address
removed, an index after the splice is decremented, a selection in another
wallet is untouched, and AUTISTMASK_ACTIVE_CHANGED is broadcast when the
active address moves so a connected site stops being told about an address
the user removed.

The wallet's derivation counter is a high-water mark and is not rewound, so
"+" derives a fresh index rather than handing back the address just removed.

src/popup/views/helpers.js

@@ -25,6 +25,7 @@ const VIEWS = [
     "add-token",
     "settings",
     "delete-wallet-confirm",
+    "delete-address-confirm",
     "settings-addtoken",
     "transaction",
     "approve-site",