feat(ui): friendly RPC errors + pause-on-hover/ellipsis toasts

Two of the systemic error-surfacing foundations from the UX audit:

- util::friendlyRpcError() maps the common raw daemon/JSON-RPC errors
  (warming up / -28, locked / -13, method-not-found / -32601, insufficient
  funds, unreachable node) to short translated guidance with a next step,
  falling back to the trimmed raw text. Wired into the send (money) path: the
  toast shows the friendly cause, the overlay keeps the raw text below it for
  diagnostics. The helper is reusable for the remaining raw-error sites.
- Toasts now pause their auto-dismiss while hovered and ellipsize over-long
  text with the full message in a hover tooltip, instead of hard-clipping it
  mid-word (durations were already lengthened earlier).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.h

@@ -79,6 +79,16 @@ inline const char* tr(const char* key) {
     return I18n::instance().translate(key);
 }
 
+/**
+ * @brief Map a raw daemon / JSON-RPC error string to a short, friendly, TRANSLATED explanation.
+ *
+ * Recognizes the common cases a user actually hits — a warming-up node, a locked wallet, an RPC the
+ * daemon is too old to have, insufficient funds, and an unreachable node — and returns plain guidance
+ * with a next step. Falls back to the raw text (trimmed) when nothing matches, so detail is never lost.
+ * Keep the raw text available elsewhere (a Details view / the console) for diagnostics.
+ */
+std::string friendlyRpcError(const std::string& raw);
+
 } // namespace util
 } // namespace dragonx