feat: short names in side bar

DocGen4/Output/Base.lean

@@ -108,7 +108,7 @@ def moduleNameToLink (n : Name) : BaseHtmlM String := do
 Returns the HTML doc-gen4 link to a module name.
 -/
 def moduleToHtmlLink (module : Name) : BaseHtmlM Html := do
-  pure <a href={←moduleNameToLink module}>{module.toString}</a>
+  pure <a href={←moduleNameToLink module}>{module.getString!}</a>
 
 /--
 Returns the LeanInk link to a module name.

DocGen4/Output/Navbar.lean

@@ -33,7 +33,7 @@ partial def moduleListDir (h : Hierarchy) : BaseHtmlM Html := do
     if h.isFile then
       <summary>{←moduleToHtmlLink h.getName}</summary>
     else
-      <summary>{h.getName.toString}</summary>
+      <summary>{h.getName.getString!}</summary>
 
   pure
     <details class="nav_sect" "data-path"={moduleLink} [if (←getCurrentName).any (h.getName.isPrefixOf ·) then #[("open", "")] else #[]]>