ui: stale tooltip wording

The dock button's tooltip, the guided-tour menu row's tooltip and the m / g shortcut labels still described a side panel and tabs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui/header-bar.ui

@@ -47,7 +47,7 @@
     <child type="end">
       <object class="GtkToggleButton" id="sidebar_toggle">
         <property name="icon-name">sidebar-show-symbolic</property>
-        <property name="tooltip-text" translatable="yes">show the side panel</property>
+        <property name="tooltip-text" translatable="yes">show the dock</property>
         <property name="active">1</property>
       </object>
     </child>