[Client] Alt badges, breadcrumb trail, investigate button (#7516)

* [Client] Alt badges, breadcrumb trail, investigate button

AltTableDelegate paints palette-tinted match badges with paint-through selection, style warning/critical icons on nonzero counts, and font/elision handling. TabAlts gains a clickable breadcrumb trail, an Investigate-this-user button, and bold usernames. Async alts responses are guarded against stale investigations.

* [Client] Fix alt badge and trail review findings

- Drop the dead VPN warning branch: rowVisible() already hides IP rows
  above the threshold, so setVpnThreshold(), its member and the spin-box
  connect never took effect.
- Dim IP rows at shared_count > 2 instead of > 1: the count already
  includes the investigated account, so every IP row was dimmed.
- Truncate backStack when a breadcrumb is clicked instead of pushing the
  current user again, so the trail keeps a single path and Back works.
- Word-wrap the trail label so a long chain cannot widen the tab.
- Extract the status/match pill painting into widgets/utility/pill_painter
  and use it from both delegates instead of duplicating it.

* [Client] Route investigate() through the trail helper

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/widgets/utility/pill_painter.cpp

@@ -0,0 +1,41 @@
+#include "pill_painter.h"
+
+#include <QApplication>
+#include <QFontMetrics>
+#include <QPainter>
+#include <QRect>
+#include <QStyle>
+#include <QStyleOptionViewItem>
+
+namespace
+{
+constexpr qreal PILL_ALPHA = 0.30;
+} // namespace
+
+bool pill_painter::paint(QPainter *painter,
+                         const QStyleOptionViewItem &option,
+                         QPalette::ColorRole tintRole,
+                         QPalette::ColorRole textRole,
+                         const QString &text)
+{
+    const QRect pillRect = option.rect.adjusted(PAD_X / 2, PAD_Y / 2, -PAD_X / 2, -PAD_Y / 2);
+    if (pillRect.width() <= 0 || pillRect.height() <= 0) {
+        return false;
+    }
+
+    if ((option.state & QStyle::State_Selected) == 0) {
+        painter->save();
+        painter->setRenderHint(QPainter::Antialiasing, true);
+        QColor pill = option.palette.color(tintRole);
+        pill.setAlphaF(PILL_ALPHA);
+        painter->setPen(Qt::NoPen);
+        painter->setBrush(pill);
+        painter->drawRoundedRect(pillRect, pillRect.height() / 2.0, pillRect.height() / 2.0);
+        painter->restore();
+    }
+
+    QStyle *style = option.widget != nullptr ? option.widget->style() : QApplication::style();
+    const QString elided = option.fontMetrics.elidedText(text, option.textElideMode, pillRect.width());
+    style->drawItemText(painter, pillRect, Qt::AlignCenter, option.palette, true, elided, textRole);
+    return true;
+}