fix(ui): escape the literal @ in the Minibits address label

Root cause of "click Receive, click Ecash, the modal disappears" (in
both the browser and the Android companion's WebView, since both host
the same neode-ui bundle): vue-i18n treats a bare @ as the start of
"linked message" syntax. receiveBitcoin.lnAddressLabel ("Your
@minibits.cash address:") isn't valid linked-message syntax, so
*compiling* that message throws a SyntaxError the instant it's first
rendered — i.e. the moment wallet.ecash-lnaddress resolves and the
address section becomes visible. The uncaught render-function error
blanks the whole teleported modal, which is indistinguishable from it
just closing.

Confirmed with a real (non-mocked) Vue app + real vue-i18n compiler in
a headless Chromium — a Vitest run with `t` mocked to a no-op, which is
how the existing component test suite covers this file, cannot catch a
bad message string at all. Fixed by escaping the @ as {'@'} — the same
pattern the codebase already uses for settings.domainNamePlaceholder
("user{'@'}example.com"). Added a regression test using the real
vue-i18n instance instead of the mocked one; verified it fails on the
old string and passes on the fix.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EawZPP9iidXj6Tvg3EpG3a

neode-ui/src/locales/en.json

@@ -777,7 +777,7 @@
     "pasteEcashToken": "Paste ecash token",
     "lnAddressTitle": "Or share your Minibits Lightning address",
     "lnAddressHint": "Anyone can pay you sats with any Lightning wallet by sending to this address — the sats arrive as ecash. Keep this screen open to receive them.",
-    "lnAddressLabel": "Your @minibits.cash address:",
+    "lnAddressLabel": "Your {'@'}minibits.cash address:",
     "lnAddressLoading": "Setting up your Lightning address…",
     "lnAddressUnavailable": "Lightning address unavailable — you can still paste a token below.",
     "lnAddressReceived": "Received {amount} sats to your Lightning address!",