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/kv.py

@@ -0,0 +1,13 @@
+from __future__ import annotations
+from datetime import datetime
+from sqlalchemy import String, Text, DateTime
+from sqlalchemy.orm import Mapped, mapped_column
+from db.base import Base
+
+class KV(Base):
+    __tablename__ = "kv"
+    """Simple key-value table for settings/cache/demo."""
+    key: Mapped[str] = mapped_column(String(120), primary_key=True)
+    value: Mapped[str | None] = mapped_column(Text(), nullable=True)
+    updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, default=datetime.utcnow, onupdate=datetime.utcnow)
+