Externalize sexp component templates and delete redundant HTML fragments

Move 24 defcomp definitions from Python string constants in components.py
to 7 grouped .sexp files under shared/sexp/templates/. Add load_sexp_dir()
to jinja_bridge.py for file-based loading. Migrate events and market
link-card fragment handlers from render_template to sexp. Delete 9
superseded Jinja HTML fragment templates.

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

account/templates/fragments/auth_menu.html

@@ -1,36 +0,0 @@
-{# Desktop auth menu #}
-<span id="auth-menu-desktop" class="hidden md:inline-flex">
-{% if user_email %}
-  <a
-    href="{{ account_url('/') }}"
-    class="justify-center cursor-pointer flex flex-row items-center p-3 gap-2 rounded bg-stone-200 text-black"
-    data-close-details
-  >
-    <i class="fa-solid fa-user"></i>
-    <span>{{ user_email }}</span>
-  </a>
-{% else %}
-  <a
-    href="{{ account_url('/') }}"
-    class="justify-center cursor-pointer flex flex-row items-center p-3 gap-2 rounded bg-stone-200 text-black"
-    data-close-details
-  >
-    <i class="fa-solid fa-key"></i>
-    <span>sign in or register</span>
-  </a>
-{% endif %}
-</span>
-{# Mobile auth menu #}
-<span id="auth-menu-mobile" class="block md:hidden text-md font-bold">
-{% if user_email %}
-  <a href="{{ account_url('/') }}" data-close-details>
-    <i class="fa-solid fa-user"></i>
-    <span>{{ user_email }}</span>
-  </a>
-{% else %}
-  <a href="{{ account_url('/') }}">
-    <i class="fa-solid fa-key"></i>
-    <span>sign in or register</span>
-  </a>
-{% endif %}
-</span>