fix(symbols): add CORS headers to symbol file responses

FileResponse does not properly include CORS headers when served from
a different origin. This fix manually adds the Access-Control-Allow-Origin
header based on the request origin.

Fixes CORS policy errors when accessing symbol files from frontend
applications running on localhost:4200 or other origins.

gns3server/api/routes/controller/symbols.py

@@ -61,7 +61,7 @@ def get_symbols() -> List[dict]:
     # FIXME: this is a temporary workaround due to a bug in the web-ui: https://github.com/GNS3/gns3-web-ui/issues/1466
     # dependencies=[Depends(has_privilege("Symbol.Audit"))]
 )
-async def get_symbol(symbol_id: str) -> FileResponse:
+async def get_symbol(symbol_id: str, request: Request) -> Response:
     """
     Download a symbol file.
 
@@ -71,7 +71,12 @@ async def get_symbol(symbol_id: str) -> FileResponse:
     controller = Controller.instance()
     try:
         symbol = controller.symbols.get_path(symbol_id)
-        return FileResponse(symbol)
+        return FileResponse(
+            symbol,
+            headers={
+                "Access-Control-Allow-Origin": request.headers.get("origin", "*"),
+            }
+        )
     except (KeyError, OSError) as e:
         raise ControllerNotFoundError(f"Could not get symbol file: {e}")