feat(ui): large-wallet nudge as a one-time toast + clickable alert

Extend the wallet-bloat warning beyond the Settings banner: when wallet.dat
first crosses 500 MB (full-node, synced), fire a one-time warning toast plus a
clickable "Consolidate notes…" entry in the bell/alerts panel that opens Merge
to Address. The persisted large_wallet_warned flag keeps it once-only and
re-arms if the file later shrinks back under the threshold.

- AlertRecord gains an optional onClick + actionHint; Notifications::action()
  pushes a toast and a clickable history entry. renderAlertHistoryPanel() now
  renders the accent action link (under the message) and measures true content
  height so wrapped messages + the link aren't clipped.
- App::maybeWarnLargeWallet() (mirrors maybeRemindSeedBackup) runs once per
  launch from update(); reuses the existing wallet_size_warn/consolidate strings.

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

src/ui/notifications.h

@@ -31,6 +31,8 @@ struct AlertRecord {
     std::string      message;
     NotificationType type;
     std::int64_t     epoch;  // std::time(nullptr) at push — wall-clock, for relative-age display
+    std::function<void()> onClick;     // optional: makes this bell-panel entry actionable
+    std::string      actionHint;       // optional: accent link label rendered for the action
 };
 
 struct Notification {
@@ -92,15 +94,25 @@ public:
         if (duration < 0.0f) duration = schemaDuration("duration-error", 4.0f);
         push(message, NotificationType::Error, duration);
     }
+
+    // An actionable alert: a normal toast PLUS a clickable entry in the bell/alert-history panel.
+    // onClick fires when the user clicks the accent `actionHint` link in that panel.
+    void action(const std::string& message, NotificationType type, std::function<void()> onClick,
+                const std::string& actionHint, float duration = -1.0f) {
+        if (duration < 0.0f) duration = schemaDuration("duration-warning", 3.5f);
+        push(message, type, duration, std::move(onClick), actionHint);
+    }
     
-    void push(const std::string& message, NotificationType type, float duration = 5.0f) {
+    void push(const std::string& message, NotificationType type, float duration = 5.0f,
+              std::function<void()> onClick = nullptr, const std::string& actionHint = "") {
         notifications_.emplace_back(message, type, duration);
 
         // Retain a copy in the persistent history (the toast above will fade in seconds; this
         // survives so the user can review what happened). Thread note: every push is on the UI
         // thread (RPC results run as main-thread MainCb callbacks), so this container needs no lock,
         // consistent with the rest of this class. Do NOT push from a raw worker thread.
-        history_.push_back(AlertRecord{message, type, static_cast<std::int64_t>(std::time(nullptr))});
+        history_.push_back(AlertRecord{message, type, static_cast<std::int64_t>(std::time(nullptr)),
+                                       std::move(onClick), actionHint});
         ++total_pushed_;
         while (history_.size() > kMaxHistory) {
             history_.pop_front();