feat: extract shared infrastructure from shared_lib

Phase 1-3 of decoupling plan:
- Shared DB, models, infrastructure, browser, config, utils
- Event infrastructure (domain_events outbox, bus, processor)
- Structured logging
- Generic container concept (container_type/container_id)
- Alembic migrations for all schema changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infrastructure/http_utils.py

@@ -0,0 +1,49 @@
+"""
+HTTP utility helpers shared across apps.
+
+Extracted from browse/services/services.py so order/orders blueprints
+(which live in the cart app) don't need to import from the browse blueprint.
+"""
+from __future__ import annotations
+
+from urllib.parse import urlencode
+
+from quart import g, request
+from shared.utils import host_url
+
+
+def vary(resp):
+    """
+    Ensure HX-Request and X-Origin are part of the Vary header
+    so caches distinguish HTMX from full-page requests.
+    """
+    v = resp.headers.get("Vary", "")
+    parts = [p.strip() for p in v.split(",") if p.strip()]
+    for h in ("HX-Request", "X-Origin"):
+        if h not in parts:
+            parts.append(h)
+    if parts:
+        resp.headers["Vary"] = ", ".join(parts)
+    return resp
+
+
+def current_url_without_page():
+    """
+    Return the current URL with the ``page`` query-string parameter removed.
+    Used for Hx-Push-Url headers on paginated routes.
+    """
+    (request.script_root or "").rstrip("/")
+    root2 = "/" + g.root
+    path_only = request.path
+
+    if root2 and path_only.startswith(root2):
+        rel = path_only[len(root2):]
+        rel = rel if rel.startswith("/") else "/" + rel
+    else:
+        rel = path_only
+    base = host_url(rel)
+
+    params = request.args.to_dict(flat=False)
+    params.pop("page", None)
+    qs = urlencode(params, doseq=True)
+    return f"{base}?{qs}" if qs else base