Fix sidebar scroll again and add missing footer back

[st0012]

1. In #1152 I only added footer to index.html but forgot about other pages. So I added it back to them in this PR.

2. I standardized sidebar nav's structure to be:

   <nav id="navigation" role="navigation">
     <div id="project-navigation">
       <%= render '_sidebar_navigation.rhtml' %>
       <%= render '_sidebar_search.rhtml' %>
     </div>
     <!-- if the page originally has it -->
     <%= render '_sidebar_table_of_contents.rhtml' %>
   
     <!-- sidebar content for the page -->
   
     <%= render '_footer.rhtml' %>
   </nav>

   And removed unnecessary divs like #project-metadata or #class-metadata as they were never referenced

3. I changed nav's default overflow setting to auto so we don't need to make individual elements to be scrollable.

Demo

https://github.com/user-attachments/assets/e0a12a60-36d8-40ef-a01e-1fcde8fb995f