chore: incorporate Copilot review comments

Author: itallix

application/backend/app/main.py

@@ -82,7 +82,7 @@ async def security_headers_middleware(
     request: Request,
     call_next: Callable[[Request], Awaitable[Response]],
 ) -> Response:
-    """"""
+    """Add COEP and COOP security headers to all HTTP responses."""
     response = await call_next(request)
     response.headers.setdefault("Cross-Origin-Embedder-Policy", "require-corp")
     response.headers.setdefault("Cross-Origin-Opener-Policy", "same-origin")
@@ -98,7 +98,7 @@ async def security_headers_middleware(
 
     @app.get("/", include_in_schema=False)
     @app.get("/{full_path:path}", include_in_schema=False)
-    async def serve_spa(full_path: str = "") -> FileResponse:  # noqa: ARG001
+    async def serve_spa() -> FileResponse:
         """Serve the Single Page Application (SPA) index.html file for any path."""
         return FileResponse(cast(Path, static_dir) / "index.html")
 

application/backend/app/settings.py

@@ -36,7 +36,11 @@ class Settings(BaseSettings):
     # Server
     host: str = Field(default="0.0.0.0", alias="HOST")  # noqa: S104
     port: int = Field(default=7860, alias="PORT")
-    static_files_dir: Path | None = None
+    static_files_dir: Path | None = Field(
+        default=None,
+        alias="STATIC_FILES_DIR",
+        description="Directory containing static UI files",
+    )
 
     # CORS
     cors_origins: str = Field(