Filter future-dated posts from public views and add unfiltered post access

- all_posts/0 now excludes posts where date > today
- all_tags/0 computed at runtime from filtered posts
- posts_by_tag/1 and recent_posts/1 inherit date filtering
- Add unfiltered_posts/0 to Blog macro and FakeBlog
- Add all_posts_unfiltered/0 to Registry for dashboard use

blogex/test/support/setup.ex

@@ -44,6 +44,12 @@ defmodule Blogex.Test.Setup do
         date: ~D[2026-03-12],
         tags: ["elixir"],
         published: false
+      ),
+      build(
+        id: "future-post",
+        date: ~D[2099-01-01],
+        tags: ["future-only"],
+        published: true
       )
     ]
   end