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/static/js/Application.js

@@ -1,6 +1,7 @@
 import { ModalManager } from "./ModalManager.js";
 import { FormManager } from "./FormManager.js";
 import { VoteManager } from "./VoteManager.js";
+import { NotificationManager } from "./NotificationManager.js";
 import { MessageSearch } from "./MessageSearch.js";
 import { ProfileEditor } from "./ProfileEditor.js";
 import { MobileNav } from "./MobileNav.js";
@@ -15,6 +16,7 @@ class Application {
         this.modals = new ModalManager();
         this.forms = new FormManager();
         this.votes = new VoteManager();
+        this.notifications = new NotificationManager();
         this.messageSearch = new MessageSearch();
         this.profile = new ProfileEditor();
         this.mobileNav = new MobileNav();