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/0000_alembic.py_

@@ -0,0 +1,20 @@
+"""Initial database schema from schema.sql"""
+
+from alembic import op
+import sqlalchemy as sa
+import pathlib
+
+# revision identifiers, used by Alembic
+revision = '0000_alembic'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+def upgrade():
+    op.execute("""
+      CREATE TABLE IF NOT EXISTS alembic_version (
+          version_num VARCHAR(32) NOT NULL,
+          CONSTRAINT alembic_version_pkc PRIMARY KEY (version_num)
+      );
+    """)
+