feat: add threaded comments with polymorphic targets and slug-based routing

Introduce `load_comments` helper supporting polymorphic target types (post, project, bug) with nested parent-child threading. Refactor comment creation to use `target_type`/`target_uid` and `resolve_target_redirect` for correct redirects. Replace raw UID-based post/project routes with slug-aware resolution via `resolve_post`/`resolve_project` and `make_combined_slug`. Update SEO, sitemap, and FAB styling to use slugs and hardcoded red accent. Add reusable `_comment_section.html` template.

devplacepy/templates/projects.html

@@ -52,7 +52,7 @@
 
         <div class="projects-grid">
             {% for project in projects %}
-            <a href="/projects/{{ project['uid'] }}" class="project-card fade-in" style="display: block; text-decoration: none; color: inherit;">
+            <a href="/projects/{{ project['slug'] or project['uid'] }}" class="project-card fade-in" style="display: block; text-decoration: none; color: inherit;">
                 <div class="project-card-header">
                     <h3 class="project-card-title">{{ project['title'] }}</h3>
                     <form method="POST" action="/votes/project/{{ project['uid'] }}" style="display:inline;">