fix: break circular import between index.py and docx_utils.py

Move the import of EXCLUDED_EMBED_METADATA_KEYS, EXCLUDED_LLM_METADATA_KEYS,
and get_heading_store to inside split_docx_into_heading_documents() to avoid
the index -> docx_utils -> index circular import at module load time.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Chetic

src/chunksilo/docx_utils.py

@@ -16,7 +16,6 @@
 from llama_index.core import Document as LlamaIndexDocument
 
 from . import cfgload
-from .index import EXCLUDED_EMBED_METADATA_KEYS, EXCLUDED_LLM_METADATA_KEYS, get_heading_store
 
 if TYPE_CHECKING:
     from .ui import FileProcessingContext
@@ -117,6 +116,9 @@ def split_docx_into_heading_documents(
         docx_path: Path to DOCX file
         ctx: Optional processing context for progress updates and timeout
     """
+    # Lazy import to avoid circular dependency (index.py imports docx_utils)
+    from .index import EXCLUDED_EMBED_METADATA_KEYS, EXCLUDED_LLM_METADATA_KEYS, get_heading_store
+
     docs: list[LlamaIndexDocument] = []
 
     if ctx: