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>

alembic/versions/0005_add_description.py

@@ -0,0 +1,27 @@
+"""Add description field to orders"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0005_add_description"
+down_revision = "0004_add_sumup_reference"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "orders",
+        sa.Column("description", sa.Text(), nullable=True),
+    )
+    op.create_index(
+        "ix_orders_description",
+        "orders",
+        ["description"],
+        unique=False,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_orders_description", table_name="orders")
+    op.drop_column("orders", "description")