feat: Add chunk-size parameters and improve file type filtering

- Add --chunk-size and --chunk-overlap parameters to all RAG examples
- Preserve original default values for each data source:
  - Document: 256/128 (optimized for general documents)
  - Email: 256/25 (smaller overlap for email threads)
  - Browser: 256/128 (standard for web content)
  - WeChat: 192/64 (smaller chunks for chat messages)
- Make --file-types optional filter instead of restriction in document_rag
- Update README to clarify interactive mode and parameter usage
- Fix LLM default model documentation (gpt-4o, not gpt-4o-mini)

examples/wechat_rag.py

@@ -42,6 +42,12 @@ class WeChatRAG(BaseRAGExample):
             action="store_true",
             help="Force re-export of WeChat data even if exports exist",
         )
+        wechat_group.add_argument(
+            "--chunk-size", type=int, default=192, help="Text chunk size (default: 192)"
+        )
+        wechat_group.add_argument(
+            "--chunk-overlap", type=int, default=64, help="Text chunk overlap (default: 64)"
+        )
 
     def _export_wechat_data(self, export_dir: Path) -> bool:
         """Export WeChat data using wechattweak-cli."""
@@ -120,7 +126,9 @@ class WeChatRAG(BaseRAGExample):
             print(f"Loaded {len(documents)} chat entries")
 
             # Convert to text chunks
-            all_texts = create_text_chunks(documents)
+            all_texts = create_text_chunks(
+                documents, chunk_size=args.chunk_size, chunk_overlap=args.chunk_overlap
+            )
 
             return all_texts