fix(custom-blocks): don't flag create as dirty when source auto-snaps

The create dirty-check compared selectedWorkspaceId against the URL
workspace, but the source picker now auto-snaps to the first workspace
the user can publish from — which may differ. Compare against that
eligible default so opening/discarding the create flow doesn't show a
false unsaved-changes state. (Bugbot)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017ddpeoz81CSqYQ73Dzf7yo

Author: TheodoreSpeaks

apps/sim/ee/custom-blocks/components/custom-block-detail.tsx

@@ -263,7 +263,7 @@ export function CustomBlockDetail({ blockId, workspaceId, onBack }: CustomBlockD
         name.trim() ||
           description.trim() ||
           selectedWorkflowId ||
-          selectedWorkspaceId !== workspaceId ||
+          selectedWorkspaceId !== eligibleDefaultWorkspaceId ||
           iconUrl ||
           visibleOutputs.length > 0 ||
           visibleInputs.some((i) => i.placeholder?.trim())