[Client] Add moderation tab with investigate, password reset, and avatar removal

- New Moderation tab: search a user to show account info, alternate
  accounts, login sessions, and staff last logins; actions to reset the
  user's password (shows the generated temporary password) and remove the
  user's avatar
- 'Investigate user' entry in the user context menu opens the tab pre-loaded
  for that user
- Warning dialog shows the infraction level of each warning category
- Tab wired into TabSupervisor with a moderator-gated menu action, shortcut,
  and tabs.ini persistence (default closed)

tests/settings/settings_defaults_test.cpp

@@ -232,6 +232,12 @@ TEST_F(SettingsDefaultsTest, Tabs_AllTabsOpen_Default)
     ASSERT_EQ(s.getTabLogOpen(), true);
 }
 
+TEST_F(SettingsDefaultsTest, Tabs_ModerationOpen_Default)
+{
+    TabsSettings s(settingsPath, nullptr);
+    ASSERT_EQ(s.getTabModerationOpen(), false);
+}
+
 // --- ChatSettings ---
 
 TEST_F(SettingsDefaultsTest, Chat_Mention_Default)