Improve image loading by handling different storage paths

Add a custom Jinja filter `image_url` to `app.py` to correctly resolve image paths from object storage or local static files, and update all relevant templates (members, sponsors, competitions, contributors) to use this new filter instead of the `url_for('static', filename=...)` function, ensuring images are displayed correctly regardless of their storage location.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: cd9a7d26-a4e5-4215-975c-c59f4ed1f06d
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: a02b1418-2e19-496d-9921-3a4afe97ac0d
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/d0a1d46d-d203-4308-bc6a-312ac7c0243b/cd9a7d26-a4e5-4215-975c-c59f4ed1f06d/05bPjFc

templates/competitions.html

@@ -26,7 +26,7 @@
                 <div class="competition-card">
                     {% if comp.image_path %}
                     <div class="competition-card-img">
-                        <img src="{{ url_for('static', filename=comp.image_path) }}">
+                        <img src="{{ comp.image_path|image_url }}">
                     </div>
                     {% endif %}
                     <div class="competition-header">