Add ssg package to registry

Static site generator utilities extracted from blu-site, providing
reusable post/tag types, content reading, date sorting, and file I/O.

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

index.json

@@ -71,6 +71,14 @@
       "versions": [
         {"version": "0.1.0", "checksum": "", "published_at": "2026-02-24", "yanked": false}
       ]
+    },
+    {
+      "name": "ssg",
+      "description": "Static site generator utilities for Lux",
+      "latest_version": "0.1.0",
+      "versions": [
+        {"version": "0.1.0", "checksum": "", "published_at": "2026-02-24", "yanked": false}
+      ]
     }
   ]
 }