Pass config file path as sourceFilename in stackConfigFileExportsConfig

Uses the previously-unused filePath param as Babel's sourceFilename so parse
diagnostics reference the real file. Addresses Copilot review note.

Co-Authored-By: mantra <mantra@stack-auth.com>

packages/stack-shared/src/stack-config-file.ts

@@ -120,6 +120,7 @@ export function stackConfigFileExportsConfig(content: string, filePath: string):
   try {
     ast = parser.parse(content, {
       sourceType: "module",
+      sourceFilename: filePath,
       plugins: ["typescript", "importAttributes"],
     });
   } catch {