refactor: use pathlib.Path for BASE_DIR, BACKEND_DIR, FRONTEND_DIR

Replaces os.path.dirname/join chains with Path(__file__).resolve() and /
operator. Updated Settings field types from str to Path to satisfy
pydantic v2 strict coercion.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/backend/settings/base.py

@@ -1,11 +1,13 @@
+from pathlib import Path
+
 from pydantic_settings import BaseSettings
 
 from backend.settings.consts import BACKEND_DIR, FRONTEND_DIR
 
 
 class Settings(BaseSettings):
-    backend_dir: str = BACKEND_DIR
-    frontend_dir: str = FRONTEND_DIR
+    backend_dir: Path = BACKEND_DIR
+    frontend_dir: Path = FRONTEND_DIR
 
     DB_URL: str = "sqlite+aiosqlite:///backend/pygentic_ai.sqlite3"
     DEBUG: bool = False

src/backend/settings/consts.py

@@ -1,13 +1,11 @@
 import enum
-import os
+from pathlib import Path
 
 from decouple import config
 
-BASE_DIR = os.path.dirname(
-    os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-)
-BACKEND_DIR = os.path.join(BASE_DIR, "backend")
-FRONTEND_DIR = os.path.join(BASE_DIR, "frontend")
+BASE_DIR = Path(__file__).resolve().parent.parent.parent
+BACKEND_DIR = BASE_DIR / "backend"
+FRONTEND_DIR = BASE_DIR / "frontend"
 
 
 pg_dialects = [