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

README.md

@@ -2036,7 +2036,9 @@ view would leave a wallet one click from deletion.
 - **Elements**:
     - "Back" button, "Delete Wallet" heading
     - Warning naming the wallet and stating that deletion is permanent and any
-      funds are unrecoverable without the recovery phrase
+      funds are unrecoverable without the recovery phrase, the private key or
+      the extended private key, according to the wallet's kind
+      (`keyMaterialName()` in `src/popup/views/helpers.js`)
     - Password input
     - Error line
     - "Confirm Delete" button
@@ -2077,9 +2079,10 @@ view would leave a wallet one click from deletion.
       cannot be unlocked again, and that no password is needed to delete it
     - What deletion does and does not do: it erases the copy of the key stored
       on this device; nothing on chain changes and no money is moved
-    - The route back — adding the wallet again with the recovery phrase and a
-      new password — and, in bold, that without that phrase written down the
-      deletion loses everything the wallet holds, forever
+    - The route back — adding the wallet again, with a new password, from a kept
+      copy of its recovery phrase, private key or extended private key (named as
+      on DeleteWallet) — and, in bold, that without that copy the deletion loses
+      everything the wallet holds, forever
     - That the other wallets are not touched
     - The wallet's name, and a text input asking for it to be typed back. A name
       that shows nothing at all (only spaces, or only characters that paint
@@ -2137,8 +2140,9 @@ view would leave a wallet one click from deletion.
       the address **only if it has on-chain activity**. An address that was
       never used is not found by that scan. The text is written by
       `recoveryPathText()` rather than sitting in `index.html`, so it can name
-      the wallet's own kind of key material: an xprv wallet has no recovery
-      phrase to re-import.
+      the wallet's own kind of key material through `keyMaterialName()`, as
+      DeleteWallet and DeleteWalletLostPassword do: an xprv wallet has no
+      recovery phrase to re-import.
     - A warning when the address holds anything, ETH or any tracked ERC-20,
       followed by the holdings themselves via `balanceLinesForAddress()` and the
       USD total via `formatAddressTotal()` (see