[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.

cockatrice/src/interface/widgets/tabs/tab_alts.h

@@ -52,6 +52,7 @@ private slots:
 
 private:
     void loadUser(const QString &userName);
+    void goToTrailEntry(const QString &userName);
     void updateTrail();
     void requestAlts(const QString &userName, int depth);
     void requestDetails(const QString &userName);