Add ty type checker to CI and fix type errors

- Add ty (Astral's fast Python type checker) to GitHub CI workflow
- Fix type annotations across all RAG apps:
  - Update load_data return types from list[str] to list[dict[str, Any]]
  - Fix base_rag_example.py to properly handle dict format from create_text_chunks
- Fix type errors in leann-core:
  - chunking_utils.py: Add explicit type annotations
  - cli.py: Fix return type annotations for PDF extraction functions
  - interactive_utils.py: Fix readline import type handling
- Fix type errors in apps:
  - wechat_history.py: Fix return type annotations
  - document_rag.py, code_rag.py: Replace **kwargs with explicit arguments
- Add ty configuration to pyproject.toml

This resolves the bug introduced in PR #157 where create_text_chunks()
changed to return list[dict] but callers were not updated.

apps/history_data/wechat_history.py

@@ -86,7 +86,7 @@ class WeChatHistoryReader(BaseReader):
                 text=True,
                 timeout=5,
             )
-            return result.returncode == 0 and result.stdout.strip()
+            return result.returncode == 0 and bool(result.stdout.strip())
         except Exception:
             return False
 
@@ -314,7 +314,7 @@ class WeChatHistoryReader(BaseReader):
 
         return concatenated_groups
 
-    def _create_concatenated_content(self, message_group: dict, contact_name: str) -> str:
+    def _create_concatenated_content(self, message_group: dict, contact_name: str) -> tuple[str, str]:
         """
         Create concatenated content from a group of messages.