Slim down README: features to a blog post, docs pointer, ASCII banner

Features section becomes a "Novaconium Features" blog post
(App/pages/blog/novaconium-features/), demonstrating the framework's own
content model rather than living as a long bullet list in README.md.
Getting started is trimmed to the minimum needed to run the site and
reach /admin/docs, which is now the single canonical source for every
topic (Docker, deploying, project layout, etc.) instead of being
mirrored into README.md. Third-party section kept as-is. AGENTS.md's
documentation-duplication rule updated to describe this new split so
future changes don't re-bloat the README. Also adds an ASCII art banner
above the title.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

App/pages/blog/index.php

@@ -40,5 +40,11 @@ return [
             'excerpt'   => 'How syntax highlighting works on this site, with worked examples in bash, HTML, CSS, YAML, Python, JavaScript, JSON, and INI/env.',
             'published' => '2026-07-14',
         ],
+        [
+            'slug'      => 'novaconium-features',
+            'title'     => 'Novaconium Features',
+            'excerpt'   => 'A tour of what ships with novaconium out of the box: routing, sidecars, caching, admin auth, access control, media manager, database, search, RSS, and more.',
+            'published' => '2026-07-15',
+        ],
     ],
 ];