refactor: Replace generator with enhanced version

- Extracts full frontmatter metadata (originalDate, notion_*, authors, source)
- Correct date priority: frontmatter → filename → mtime → ctime
- All metadata exposed in index.json for frontend use

Phase 1 quick win complete.

package.json

@@ -2,6 +2,6 @@
   "name": "the-fold-within",
   "version": "3.0.2",
   "dependencies": {
-    "pdf-parse": "^1.1.1"
+    "pdf-parse": "^1.1.4"
   }
 }