fix: the delete wallet screens name the wallet's own key material (closes #529)

DeleteWallet and DeleteWalletLostPassword told key and xprv wallets that
their recovery phrase was the way back, but those wallets have none. Both
screens now name the recovery phrase, the private key or the extended
private key, according to the wallet's kind.

The noun comes from keyMaterialName() in the popup view helpers, which
DeleteAddress now uses too in place of its own two-way choice, so these
three screens get it from one place. The lost-password screen's route-back
sentence is reworded to fit all three kinds.

Model: opus-5-5

src/popup/index.html

@@ -1123,7 +1123,8 @@
                 <p class="text-xs mb-3">
                     Deleting
                     <strong id="delete-wallet-name"></strong> is permanent. Any
-                    funds will be unrecoverable without your recovery phrase.
+                    funds will be unrecoverable without your
+                    <span id="delete-wallet-key-material"></span>.
                 </p>
                 <div class="mb-2">
                     <label class="block mb-1">Password</label>
@@ -1174,13 +1175,13 @@
                     money at its addresses is not moved or destroyed.
                 </p>
                 <p class="text-xs mb-2">
-                    If you have the recovery phrase for this wallet written
-                    down, add the wallet again afterwards with a new password
-                    and you will have it back.
+                    If you have kept a copy of this wallet's
+                    <span id="delete-wallet-lost-key-material"></span>, add the
+                    wallet again afterwards with a new password and you will
+                    have it back.
                     <strong
-                        >If you do not have it written down, deleting this
-                        wallet means losing everything it holds,
-                        forever.</strong
+                        >If you have not, deleting this wallet means losing
+                        everything it holds, forever.</strong
                     >
                 </p>
                 <p class="text-xs mb-3">Your other wallets are not touched.</p>