feat(diagnostics): persistent alert history with a status-bar bell (Foundation QoL)

Toasts fade in 1-4s, so anything that scrolled past was gone. Notifications now retains
every pushed alert in a capped (100) ring buffer with a wall-clock epoch (AlertRecord) —
separate from the 5-item live-toast deque — plus a monotonic total_pushed_ counter.

A bell in the status-bar right cluster opens an upward popup listing recent alerts
newest-first: severity icon + colour (reusing the toast palette), the message, and a
relative age (formatTimeAgoShort), with a Clear-all action. An unread dot on the bell,
coloured by the most-severe unseen alert, marks alerts that arrived since the panel was
last opened — driven by totalPushed() deltas so it survives capping/clearing.

Thread note: every push is on the UI thread (RPC results run as main-thread MainCb
callbacks), matching this class's existing lock-free model; documented as a
no-raw-worker-thread invariant.

New i18n keys (alerts_*). Build-clean; ctest 1/1 (adds testNotificationHistory: retention,
order, cap, monotonic counter, clear). Closes the QoL bundle and the Foundation tier.

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

src/ui/notifications.h

@@ -9,6 +9,8 @@
 #include <chrono>
 #include <functional>
 #include <cstdio>
+#include <cstdint>
+#include <ctime>
 #include "../util/logger.h"
 #include "schema/ui_schema.h"
 
@@ -22,6 +24,15 @@ enum class NotificationType {
     Error
 };
 
+// A retained alert for the persistent history panel. Unlike a live Notification (which fades and is
+// erased within seconds), this keeps a wall-clock epoch so its age can be shown as "3m ago" long
+// after the toast is gone. See App::renderAlertHistoryPanel.
+struct AlertRecord {
+    std::string      message;
+    NotificationType type;
+    std::int64_t     epoch;  // std::time(nullptr) at push — wall-clock, for relative-age display
+};
+
 struct Notification {
     std::string message;
     NotificationType type;
@@ -84,20 +95,30 @@ public:
     
     void push(const std::string& message, NotificationType type, float duration = 5.0f) {
         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))});
+        ++total_pushed_;
+        while (history_.size() > kMaxHistory) {
+            history_.pop_front();
+        }
+
         // Log errors and warnings (debug-only output)
         if (type == NotificationType::Error) {
             DEBUG_LOGF("[ERROR] Notification: %s\n", message.c_str());
         } else if (type == NotificationType::Warning) {
             DEBUG_LOGF("[WARN] Notification: %s\n", message.c_str());
         }
-        
+
         // Forward errors and warnings to console callback
         if (console_callback_ && (type == NotificationType::Error || type == NotificationType::Warning)) {
             const char* prefix = (type == NotificationType::Error) ? "[ERROR] " : "[WARN] ";
             console_callback_(prefix + message, type == NotificationType::Error);
         }
-        
+
         // Limit max notifications
         while (notifications_.size() > max_notifications_) {
             notifications_.pop_front();
@@ -122,21 +143,34 @@ public:
     void clear() {
         notifications_.clear();
     }
-    
+
     void setMaxNotifications(size_t max) {
         max_notifications_ = max;
     }
-    
+
+    // ── Persistent alert history (for the status-bar bell panel) ──
+    /// Retained alerts, oldest first (capped at kMaxHistory; the toast deque is separate).
+    const std::deque<AlertRecord>& history() const { return history_; }
+    bool hasHistory() const { return !history_.empty(); }
+    void clearHistory() { history_.clear(); }
+    /// Monotonic count of every alert ever pushed this session — survives capping/clearing, so it is
+    /// the correct basis for an "unseen since last opened" count (deque size is not).
+    std::uint64_t totalPushed() const { return total_pushed_; }
+
 private:
     Notifications() = default;
     ~Notifications() = default;
     Notifications(const Notifications&) = delete;
     Notifications& operator=(const Notifications&) = delete;
-    
+
     std::deque<Notification> notifications_;
     size_t max_notifications_ = 5;
     std::function<void(const std::string&, bool)> console_callback_;
 
+    std::deque<AlertRecord> history_;
+    std::uint64_t total_pushed_ = 0;
+    static constexpr size_t kMaxHistory = 100;
+
     static float schemaDuration(const char* key, float fallback) {
         float v = schema::UI().drawElement("components.notifications", key).size;
         return v > 0.0f ? v : fallback;