Fix nested raw! sexp errors and missing container nav in market pages

- Fix invalid nested (raw! a (raw! b)) patterns in market and events
  sexp_components — concatenate HTML strings in Python, pass single
  var to (raw! h) instead
- Add container_nav_html fetch to market inject_post context processor
  so page-scoped market pages show calendar/market nav links
- Add qs_filter to base_context for sexp filter URL building

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

market/app.py

@@ -199,7 +199,24 @@ def create_app() -> "Quart":
         post_data = getattr(g, "post_data", None)
         if not post_data:
             return {}
-        return {**post_data}
+        ctx = {**post_data}
+        # Fetch container nav fragments (calendar + market links for this page)
+        post_dict = post_data.get("post") or {}
+        db_post_id = post_dict.get("id")
+        post_slug = post_dict.get("slug", "")
+        if db_post_id:
+            from shared.infrastructure.fragments import fetch_fragments
+            nav_params = {
+                "container_type": "page",
+                "container_id": str(db_post_id),
+                "post_slug": post_slug,
+            }
+            events_nav, market_nav = await fetch_fragments([
+                ("events", "container-nav", nav_params),
+                ("market", "container-nav", nav_params),
+            ], required=False)
+            ctx["container_nav_html"] = events_nav + market_nav
+        return ctx
 
     # --- oEmbed endpoint ---
     @app.get("/oembed")