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/static/css/feed.css

@@ -323,13 +323,13 @@
     width: 56px;
     height: 56px;
     border-radius: 50%;
-    background: var(--accent);
+    background: #e53935;
     color: #fff;
     font-size: 1.5rem;
     display: flex;
     align-items: center;
     justify-content: center;
-    box-shadow: 0 4px 16px rgba(255, 107, 53, 0.4);
+    box-shadow: 0 4px 16px rgba(229, 57, 53, 0.4);
     transition: all 0.2s;
     z-index: 100;
     border: none;
@@ -337,9 +337,9 @@
 }
 
 .feed-fab:hover {
-    background: var(--accent-hover);
+    background: #c62828;
     transform: scale(1.05);
-    box-shadow: 0 6px 20px rgba(255, 107, 53, 0.5);
+    box-shadow: 0 6px 20px rgba(229, 57, 53, 0.5);
 }
 
 .feed-comment-form {