Remove cross-domain template dependencies from shared infrastructure

- macros/search.html: shared search input macros (mobile + desktop)
- macros/cart_icon.html: shared cart icon/badge macro (count param, no DB)
- macros/layout.html: inline hamburger icon, use shared search macro
- _oob.html: use cart_mini_html fragment slot instead of cart template import
- db/session.py: guard teardown rollback against committed/dead sessions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

browser/templates/macros/layout.html

@@ -26,7 +26,17 @@
   <summary class="bg-white/90">
     <div class="flex flex-row items-start">
       <div>
-        {% include '_types/blog/mobile/_filter/_hamburger.html' %}
+        <div class="md:hidden mx-2 bg-stone-200 rounded">
+          <span class="flex items-center justify-center text-stone-600 text-lg h-12 w-12 transition-transform group-open/filter:hidden self-start">
+            <i class="fa-solid fa-filter"></i>
+          </span>
+          <span>
+            <svg aria-hidden="true" viewBox="0 0 24 24"
+                  class="w-12 h-12 rotate-180 transition-transform group-open/filter:block hidden self-start">
+              <path d="M6 9l6 6 6-6" fill="currentColor"/>
+            </svg>
+          </span>
+        </div>
       </div>
       <div
         id="{{id}}"
@@ -37,8 +47,8 @@
 
         </div>
       </div>
-      {% import '_types/browse/mobile/_filter/search.html' as s %}
-      {{ s.search(current_local_href, search, search_count, hx_select) }}
+      {% from 'macros/search.html' import search_mobile %}
+      {{ search_mobile(current_local_href, search, search_count, hx_select) }}
     </div>
   </summary>
 {%- endmacro %}