feat: add path helper functions to file_service

- get_app_dir(): project root in dev, exe dir in PyInstaller bundle
- get_resource_path/get_config_path: paths under app dir
- get_log_dir/get_output_dir: auto-create and return logs/ and output/
- Refactor log_service to use get_log_dir() instead of own __file__ calc

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

src/services/file_service.py

@@ -1,5 +1,51 @@
+import logging
+import sys
+from pathlib import Path
+
+logger = logging.getLogger(__name__)
+
 SUPPORTED_IMAGE_EXTENSIONS = {".png", ".jpg", ".jpeg", ".webp"}
 
 
 def is_supported_image(path):
     return path.suffix.lower() in SUPPORTED_IMAGE_EXTENSIONS
+
+
+# ---------------------------------------------------------------------------
+# Path helpers
+# ---------------------------------------------------------------------------
+
+def get_app_dir():
+    """Return the application root directory as a Path.
+
+    PyInstaller onedir: directory that contains the .exe.
+    Development: project root (three levels above this file:
+        src/services/file_service.py -> src/services -> src -> project root).
+    """
+    if getattr(sys, "frozen", False):
+        return Path(sys.executable).resolve().parent
+    return Path(__file__).resolve().parent.parent.parent
+
+
+def get_resource_path(relative_path):
+    """Return absolute Path for a file under <app_dir>/resources/."""
+    return get_app_dir() / "resources" / relative_path
+
+
+def get_config_path(relative_path):
+    """Return absolute Path for a file under <app_dir>/config/."""
+    return get_app_dir() / "config" / relative_path
+
+
+def get_log_dir():
+    """Return <app_dir>/logs/ as a Path, creating the directory if absent."""
+    d = get_app_dir() / "logs"
+    d.mkdir(exist_ok=True)
+    return d
+
+
+def get_output_dir():
+    """Return <app_dir>/output/ as a Path, creating the directory if absent."""
+    d = get_app_dir() / "output"
+    d.mkdir(exist_ok=True)
+    return d