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>

requirements.txt

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+starlette>=0.37,<0.39
+aiofiles==25.1.0
+aiosmtplib==5.0.0
+alembic==1.17.0
+anyio==4.11.0
+async-timeout==5.0.1
+asyncpg==0.30.0
+beautifulsoup4==4.14.2
+blinker==1.9.0
+Brotli==1.1.0
+certifi==2025.10.5
+click==8.3.0
+exceptiongroup==1.3.0
+Flask==3.1.2
+greenlet==3.2.4
+h11==0.16.0
+h2==4.3.0
+hpack==4.1.0
+httpcore==1.0.9
+httpx==0.28.1
+Hypercorn==0.17.3
+hyperframe==6.1.0
+idna==3.10
+itsdangerous==2.2.0
+Jinja2==3.1.6
+lxml==6.0.2
+Mako==1.3.10
+MarkupSafe==3.0.3
+priority==2.0.0
+psycopg==3.2.11
+psycopg-binary==3.2.11
+PyJWT==2.10.1
+PyYAML==6.0.3
+Quart==0.20.0
+sniffio==1.3.1
+soupsieve==2.8
+SQLAlchemy==2.0.44
+taskgroup==0.2.2
+tomli==2.3.0
+typing_extensions==4.15.0
+Werkzeug==3.1.3
+wsproto==1.2.0
+zstandard==0.25.0
+redis>=5.0
+mistune>=3.0
+pytest>=8.0
+pytest-asyncio>=0.23