feat(backend): add FastAPI app entry point

backend/src/config.py

@@ -0,0 +1,27 @@
+from functools import lru_cache
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(
+        env_file=".env",
+        env_file_encoding="utf-8",
+        case_sensitive=False,
+    )
+
+    app_name: str = "CodeTutor API"
+    app_version: str = "0.1.0"
+    debug: bool = False
+
+    database_url: str
+
+    cors_origins: list[str] = ["http://localhost:3000"]
+
+    default_page_size: int = 20
+    max_page_size: int = 100
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()