feat: extract shared infrastructure from shared_lib

Phase 1-3 of decoupling plan:
- Shared DB, models, infrastructure, browser, config, utils
- Event infrastructure (domain_events outbox, bus, processor)
- Structured logging
- Generic container concept (container_type/container_id)
- Alembic migrations for all schema changes

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

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)