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/app/__init__.py

@@ -0,0 +1,12 @@
+# The monolith has been split into three apps (apps/coop, apps/market, apps/cart).
+# This package remains for shared infrastructure modules (middleware, redis_cacher,
+# csrf, errors, authz, filters, utils, bp/*).
+#
+# To run individual apps:
+#   hypercorn apps.coop.app:app --bind 0.0.0.0:8000
+#   hypercorn apps.market.app:app --bind 0.0.0.0:8001
+#   hypercorn apps.cart.app:app --bind 0.0.0.0:8002
+#
+# Legacy single-process:
+#   hypercorn suma_browser.app.app:app --bind 0.0.0.0:8000
+#   (runs the old monolith from app.py, which still works)