fix: update run command to python -m src.main with sys.path guard

Adds src/__init__.py to make the package importable.
Updates CLAUDE.md run example to use -m invocation.

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

Author: chrisdpurcell

CLAUDE.md

@@ -11,8 +11,8 @@ TextTools is a PySide6 desktop application for text processing on Linux. Its pla
 ## Commands
 
 ```bash
-# Run the application
-python src/main.py
+# Run the application (must be run from project root)
+python -m src.main
 
 # Run all tests (coverage is on by default via pyproject.toml addopts)
 pytest tests/

src/__init__.py

@@ -6,14 +6,21 @@
 
 import logging
 import sys
+from pathlib import Path
 
-from PySide6.QtWidgets import QApplication
+# Insert project root so `from src.xxx` imports resolve regardless of how the
+# script is invoked (python src/main.py, python -m src.main, full path, IDE).
+_project_root = Path(__file__).resolve().parent.parent
+if str(_project_root) not in sys.path:
+    sys.path.insert(0, str(_project_root))
 
-from src.services.file_service import FileService
-from src.services.text_processing_service import TextProcessingService
-from src.utils.constants import APP_NAME, APP_VERSION
-from src.viewmodels.main_viewmodel import MainViewModel
-from src.views.main_window import MainWindow
+from PySide6.QtWidgets import QApplication  # noqa: E402
+
+from src.services.file_service import FileService  # noqa: E402
+from src.services.text_processing_service import TextProcessingService  # noqa: E402
+from src.utils.constants import APP_NAME, APP_VERSION  # noqa: E402
+from src.viewmodels.main_viewmodel import MainViewModel  # noqa: E402
+from src.views.main_window import MainWindow  # noqa: E402
 
 logging.basicConfig(
     level=logging.INFO,