feat(wallet): richer detail in the wallet-switch progress modal

The switch modal now shows more than a bare phase line:
- The title carries the target wallet ("Switching wallet — savings") and a
  "from <previous>" caption for context (names prettified: wallet.dat → "Default
  wallet", wallet-<name>.dat → "<name>", in-place links → "External wallet").
- During the Reconnecting phase — the ~30-60s where the node loads the block
  index, verifies, and rescans — it surfaces the node's LIVE init stage
  (state_.warmup_status/description via the existing translateWarmup mapping:
  "Loading blockchain data…", "Verifying blockchain…", "Scanning for
  transactions…") instead of a static "Reconnecting…".
- An elapsed timer (m:ss) so the wait visibly progresses.

i18n: from/elapsed/default-wallet/external-wallet labels (EN + 8 languages,
additive; no new CJK glyphs). No switch-flow logic change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -779,6 +779,7 @@ private:
     std::atomic<int>  wallet_switch_phase_{0};
     std::atomic<bool> wallet_switch_dialog_open_{false};
     std::string       wallet_switch_error_;
+    double            wallet_switch_started_time_ = 0.0;  // ImGui::GetTime() captured on first progress frame (elapsed)
 
     // Set by the deleteBlockchainData worker (item count); the main loop surfaces a completion toast
     // and resets it to -1. Atomic because the worker thread writes it and the UI thread reads/clears it.