mobile: cache-bust static assets so browser picks up CSS/JS edits

User reported phone still showing old behaviour (Qty/Avg portfolio
columns visible) even though the server-side JS had been updated.
Root cause: every <link>/<script> URL was a plain
/static/css/foo.css with no query string, so mobile Chrome served
the file from its HTTP cache rather than refetching it.

Adds a process-startup timestamp to the Jinja environment as
ASSET_VERSION (computed once when templates_env is imported). Every
<link>/<script> reference now appends `?v={{ ASSET_VERSION }}` so a
container restart bumps the URL and the browser refetches. 38 URLs
across 8 templates updated via sed; tests still pass.

Side benefit: future CSS/JS edits no longer require users to hard-
refresh.

app/templates/log.html

@@ -69,5 +69,5 @@
     {% endif %}
   </div>
 </section>
-{% if paid %}<script src="{{ url_for('static', path='/js/chat.js') }}" defer></script>{% endif %}
+{% if paid %}<script src="{{ url_for('static', path='/js/chat.js') }}?v={{ ASSET_VERSION }}" defer></script>{% endif %}
 {% endblock %}