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/menu_item.py

@@ -0,0 +1,42 @@
+from datetime import datetime
+from typing import Optional
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy import Integer, String, DateTime, ForeignKey, func
+from db.base import Base
+
+
+class MenuItem(Base):
+    __tablename__ = "menu_items"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+
+    # Foreign key to posts table
+    post_id: Mapped[int] = mapped_column(
+        Integer,
+        ForeignKey("posts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True
+    )
+
+    # Order for sorting menu items
+    sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0, index=True)
+
+    # Timestamps
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        nullable=False
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+        nullable=False
+    )
+    deleted_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime(timezone=True),
+        nullable=True
+    )
+
+    # Relationship to Post
+    post: Mapped["Post"] = relationship("Post", back_populates="menu_items")