Add line break before Usage Guidance section on spec page

Improves readability by adding visual spacing between the self-description
paragraph and the Usage Guidance heading.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: brannn

web/cmd/server/static/spec.html

@@ -833,6 +833,8 @@ <h2>Meta-Specification</h2>
                     <button class="collapsible-code-toggle" onclick="toggleCodeBlock(this)">Show full specification</button>
                     </div>
                     <p>The self-description constraint is meaningful. Any future version of Simplex must remain self-describing and pass its own linter. This provides a check on evolution: changes that break self-description or fail linting are changes that have gone too far.</p>
+
+                    <p><br></p>
                 </section>
 
                 <!-- Usage Guidance -->