fix: the StateRecovery erase warning names every kind of wallet backup (closes #593)

The erase warning told every user to rely on each wallet's recovery
phrase. A wallet imported from a private key or an extended private key
has no recovery phrase. The warning now names all three, in the words the
delete wallet screens use. The screen cannot read the wallets, so one
sentence covers every kind. README's StateRecovery entry says the same.

Model: opus-5-5

README.md

@@ -2820,6 +2820,9 @@ view would leave a wallet one click from deletion.
     - "Export Saved Data" button, and the read-only text box it fills
     - What erasing does and does not do, in bold: every wallet stored in this
       browser is deleted; nothing on chain changes and no money is moved
+    - What a wallet can be added again from: a kept copy of its recovery phrase,
+      private key or extended private key. Without that copy or the exported
+      copy, everything the wallet holds is gone forever.
     - A text input asking for `ERASE MY WALLET` to be typed back
     - Error line
     - "Erase Saved Data" button