chore(lint): allow default exports in config files

Add biome override to permit default exports in .config/ directory.
Config files require default exports for tool compatibility (ESLint,
Vitest, Taze) while the rest of the codebase uses named exports only.

Author: jdalton

biome.json

@@ -180,6 +180,16 @@
           }
         }
       }
+    },
+    {
+      "includes": [".config/**/*"],
+      "linter": {
+        "rules": {
+          "style": {
+            "noDefaultExport": "off"
+          }
+        }
+      }
     }
   ]
 }