feat: initial shared library extraction

Contains shared infrastructure for all coop services:
- shared/ (factory, urls, user_loader, context, internal_api, jinja_setup)
- models/ (User, Order, Calendar, Ticket, Product, Ghost CMS)
- db/ (SQLAlchemy async session, base)
- suma_browser/app/ (csrf, middleware, errors, authz, redis_cacher, payments, filters, utils)
- suma_browser/templates/ (shared base layouts, macros, error pages)
- static/ (CSS, JS, fonts, images)
- alembic/ (database migrations)
- config/ (app-config.yaml)
- editor/ (Lexical editor Node.js build)
- requirements.txt

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

suma_browser/templates/sentinel/mobile_content.html

@@ -0,0 +1,11 @@
+ <!-- tiny loading text (default) -->
+  <div class="js-loading text-center text-xs text-stone-400">
+    loading… {{ page }} / {{ total_pages }}
+  </div>
+
+  <!-- BIG error panel (hidden by default) -->
+  <div class="js-neterr hidden flex h-full items-center justify-center">
+    <!-- Funky SVG: unplugged cable + pulse -->
+
+    {% include "sentinel/wireless_error.svg" %}
+  </div>