Add a Wallet menu item (between File and Settings) that opens an in-app
overlay showing wallet metadata: file name, network, type (HD seed / xprv /
WIF / watch-only), script kind, derivation path, master fingerprint, and
account xpub.
Includes a seed section: if the wallet has no seed, a note is shown; if it
has one and is unencrypted the seed is revealed directly; if encrypted the
user must enter the wallet file password before the mnemonic is displayed.
The revealed seed is shown in a danger-coloured bordered box with a warning.
Closing the overlay (backdrop, Close button, or Esc) always clears the
password input and hides the seed.
Also adds the private-key password-prompt overlay and its localization keys
(shared UI scaffolding used by the following commit).
