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>

models/__init__.py

@@ -0,0 +1,21 @@
+from .kv import KV
+from .user import User
+from .magic_link import MagicLink
+from .market import ProductLike
+from .ghost_content import Author, Tag, Post, PostAuthor, PostTag, PostLike
+from .menu_item import MenuItem
+
+
+from .ghost_membership_entities import (
+    GhostLabel, UserLabel,
+    GhostNewsletter, UserNewsletter,
+    GhostTier, GhostSubscription,
+)
+
+from .calendars import Calendar, CalendarEntry, Ticket
+
+
+
+from .order import Order, OrderItem
+from .snippet import Snippet
+from .tag_group import TagGroup, TagGroupTag