fix: make python-pptx import lazy in pptx_parser to fix CI collection error

python-pptx is not in [dev] extras so it's absent in CI, causing
ModuleNotFoundError during test collection via parse/__init__.py.
Moved import inside the parse method with a clear install hint.

This is the last known bare top-level optional import — sqlalchemy
(db_ingestor.py) and pdfplumber (pdf_parser.py) were fixed in prior commits.

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

semantica/parse/pptx_parser.py

@@ -32,8 +32,6 @@ from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Any, Dict, List, Optional, Union
 
-from pptx import Presentation
-
 from ..utils.exceptions import ProcessingError, ValidationError
 from ..utils.logging import get_logger
 from ..utils.progress_tracker import get_progress_tracker
@@ -97,6 +95,13 @@ class PPTXParser:
             raise ValidationError(f"File is not a PPTX: {file_path}")
 
         try:
+            try:
+                from pptx import Presentation
+            except ImportError:
+                raise ProcessingError(
+                    "python-pptx is required for PPTX parsing. "
+                    "Install with: pip install python-pptx"
+                )
             prs = Presentation(str(file_path))
 
             # Extract metadata