fix: add missing template variables for pages listing context

The shared sidebar/filter templates expect selected_groups, tags, authors
etc. Provide empty defaults when rendering the pages view.

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

bp/blog/routes.py

@@ -90,6 +90,17 @@ def register(url_prefix, title):
               **data,
               "content_type": "pages",
               "search": q.search,
+              "selected_tags": (),
+              "selected_authors": (),
+              "selected_groups": (),
+              "sort": None,
+              "view": None,
+              "drafts": None,
+              "draft_count": 0,
+              "tags": [],
+              "authors": [],
+              "tag_groups": [],
+              "posts": data.get("pages", []),
           }
           if not is_htmx_request():
               html = await render_template("_types/blog/index.html", **context)