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>

suma_browser/app/utils/htmx.py

@@ -0,0 +1,46 @@
+"""HTMX utilities for detecting and handling HTMX requests."""
+
+from quart import request
+
+
+def is_htmx_request() -> bool:
+    """
+    Check if the current request is an HTMX request.
+
+    Returns:
+        bool: True if HX-Request header is present and true
+    """
+    return request.headers.get("HX-Request", "").lower() == "true"
+
+
+def get_htmx_target() -> str | None:
+    """
+    Get the target element ID from HTMX request headers.
+
+    Returns:
+        str | None: Target element ID or None
+    """
+    return request.headers.get("HX-Target")
+
+
+def get_htmx_trigger() -> str | None:
+    """
+    Get the trigger element ID from HTMX request headers.
+
+    Returns:
+        str | None: Trigger element ID or None
+    """
+    return request.headers.get("HX-Trigger")
+
+
+def should_return_fragment() -> bool:
+    """
+    Determine if we should return a fragment vs full page.
+
+    For HTMX requests, return fragment.
+    For normal requests, return full page.
+
+    Returns:
+        bool: True if fragment should be returned
+    """
+    return is_htmx_request()