feat(ui): add navigation layout and basic styling

Implement foundational UI components including navigation bar,
CSS styling, and improved rankings page.

Changes:
- Add navigation bar with links to Rankings, Profile, Schedule, Admin
- Add comprehensive CSS styling for tables, forms, buttons, alerts
- Improve rankings page with profile links
- Support conditional navigation based on authentication status

app/templates/players/rankings.html.erb

@@ -8,6 +8,7 @@
         <th>Player</th>
         <th>Elo Rating</th>
         <th>Original Rating</th>
+        <th>Actions</th>
       </tr>
     </thead>
     <tbody>
@@ -17,6 +18,9 @@
           <td><%= player.name %></td>
           <td><strong><%= player.current_elo %></strong></td>
           <td><%= player.rating %></td>
+          <td>
+            <a href="/players/<%= player.id %>/profile">Profile</a>
+          </td>
         </tr>
       <% end %>
     </tbody>