refactor: delete-wallet-confirm as standalone full view

Replace the inline confirmation div at the bottom of Settings with a
proper full-screen view (view-delete-wallet-confirm). This fixes the
issue where the confirmation was offscreen on the 360x600 popup.

- New view with back button, title, warning text, password input,
  and red-text Confirm Delete button
- Dedicated flash area for password errors
- New deleteWallet.js module with init/show pattern
- Added delete-wallet-confirm to VIEWS array in helpers.js
- Removed old inline confirmation HTML and logic from settings

src/popup/views/helpers.js

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