fix: properly configure redirects and clean up moved files

- Added redirects in next.config.mjs for moved concept pages
- Removed old entries from advanced/_meta.js
- Deleted the old moved files from advanced folder
- Cleaned up shallow-imgs directory from advanced folder

This ensures proper URL redirects and avoids duplicate content.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: zxch3n

next.config.mjs

@@ -72,6 +72,27 @@ export default withNextra({
         destination: '/docs/advanced/event_graph_walker',
         permanent: true,
       },
+      // Redirects for extracted concept documents
+      {
+        source: '/docs/advanced/doc_state_and_oplog',
+        destination: '/docs/concepts/oplog_docstate',
+        permanent: true,
+      },
+      {
+        source: '/docs/advanced/op_and_change',
+        destination: '/docs/concepts/operations_changes',
+        permanent: true,
+      },
+      {
+        source: '/docs/advanced/event_graph_walker',
+        destination: '/docs/concepts/event_graph_walker',
+        permanent: true,
+      },
+      {
+        source: '/docs/advanced/shallow_snapshot',
+        destination: '/docs/concepts/shallow_snapshots',
+        permanent: true,
+      },
     ]
   },
 })

pages/docs/advanced/_meta.js

@@ -1,11 +1,7 @@
 export default {
-  doc_state_and_oplog: "DocState and OpLog",
   cid: "Container ID",
-  shallow_snapshot: "Shallow Snapshot",
   timestamp: "Storing Timestamps",
-  op_and_change: "Operations and Change",
   version_deep_dive: "Loro's Versioning Deep Dive: DAG, Frontiers, and Version Vectors",
-  event_graph_walker: "Event Graph Walker",
   undo: "Undo/Redo",
   import_batch: "Batch Import",
   inspector: "Loro Inspector"