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.

packages/leann-core/src/leann/chunking_utils.py

@@ -239,8 +239,8 @@ def create_ast_chunks(
 
             chunks = chunk_builder.chunkify(code_content)
             for chunk in chunks:
-                chunk_text = None
-                astchunk_metadata = {}
+                chunk_text: str | None = None
+                astchunk_metadata: dict[str, Any] = {}
 
                 if hasattr(chunk, "text"):
                     chunk_text = chunk.text

packages/leann-core/src/leann/cli.py

@@ -19,7 +19,7 @@ from .settings import (
 )
 
 
-def extract_pdf_text_with_pymupdf(file_path: str) -> str:
+def extract_pdf_text_with_pymupdf(file_path: str) -> str | None:
     """Extract text from PDF using PyMuPDF for better quality."""
     try:
         import fitz  # PyMuPDF
@@ -35,7 +35,7 @@ def extract_pdf_text_with_pymupdf(file_path: str) -> str:
         return None
 
 
-def extract_pdf_text_with_pdfplumber(file_path: str) -> str:
+def extract_pdf_text_with_pdfplumber(file_path: str) -> str | None:
     """Extract text from PDF using pdfplumber for better quality."""
     try:
         import pdfplumber

packages/leann-core/src/leann/interactive_utils.py

@@ -11,14 +11,15 @@ from pathlib import Path
 from typing import Callable, Optional
 
 # Try to import readline with fallback for Windows
+HAS_READLINE = False
+readline = None  # type: ignore[assignment]
 try:
-    import readline
+    import readline  # type: ignore[no-redef]
 
     HAS_READLINE = True
 except ImportError:
     # Windows doesn't have readline by default
-    HAS_READLINE = False
-    readline = None
+    pass
 
 
 class InteractiveSession: