feat: replace legacy vote buttons with AJAX submission and dynamic count updates

Replace static form-based vote buttons with a new VoteManager class that submits votes via fetch, returns JSON with net/up/down/current value, and updates vote count spans using data-vote-count attributes across all templates. Add JSONResponse endpoint in votes router for AJAX requests, switch VoteManager import from Http to Toast for error feedback, and refactor link_attachments to handle comma-separated UIDs.

devplacepy/templates/project_detail.html

@@ -136,7 +136,7 @@
             {% if user %}
             <form method="POST" action="/votes/project/{{ project['uid'] }}" style="display:inline;">
                 <input type="hidden" name="value" value="1">
-                <button type="submit" class="project-star-btn">&#x2606; {{ star_count }}</button>
+                <button type="submit" class="project-star-btn">&#x2606; <span class="vote-count-value" data-vote-count="{{ project['uid'] }}">{{ star_count }}</span></button>
             </form>
             {% endif %}
             {% if is_owner %}