feat: add resolve_object_url helper and notification click-through with comment highlighting

Extract duplicate target-redirect logic from comments router into a new `resolve_object_url` database function, add `target_url` field to follow and message notifications, create `/notifications/open/{uid}` endpoint that marks notifications read and redirects to their target, implement client-side NotificationManager for card clicks and comment hash scrolling, and add comment-highlight CSS animation.

devplacepy/templates/_comment_section.html

@@ -15,7 +15,7 @@
             </form>
         </div>
 
-        <div class="comment-body" data-comment-uid="{{ item.comment['uid'] }}">
+        <div class="comment-body" id="comment-{{ item.comment['uid'] }}" data-comment-uid="{{ item.comment['uid'] }}">
             <div class="comment-header">
                 <a href="/profile/{{ item.author['username'] if item.author else '#' }}">
                 <img src="{{ avatar_url('multiavatar', item.author['username'] if item.author else '?', 32) }}" class="avatar-img avatar-sm" alt="{{ item.author['username'] if item.author else '?' }}" loading="lazy">