docs: add comprehensive package overview guide and update documentation index

Agent-Logs-Url: https://github.com/objectstack-ai/framework/sessions/0ea8718e-c180-4863-8bbb-e522375ff695

Co-authored-by: xuyushun441-sys <255036401+xuyushun441-sys@users.noreply.github.com>

Author: Claude

content/docs/guides/meta.json

@@ -2,6 +2,7 @@
   "title": "Guides",
   "pages": [
     "index",
+    "packages",
     "metadata",
     "data-modeling",
     "common-patterns",