fix(app): support CSF v3 stories in composeEnhancers (#602)

[darioabc]

Closes #602.

Background

Storybook's Component Story Format v3 (the default since Storybook 7, 2023) defines a story as a plain object:

export const Default: Story = {
  args: { variant: "primary" },
  render: (args) => <Button {...args} />,
};

Ladle today only handles CSF v2, where the named export is a React.FC with .args / .argTypes / .decorators attached as function properties. With CSF v3 stories, composeEnhancers passes the plain object to ArgsProvider, which does React.createElement(component, props) — and React 19 (and 17/18 alike) throws Element type is invalid: expected a string … or a class/function … but got: object.

Verified the failure in a 312-story production codebase — every story errored under Ladle 5.1.1 + React 19. The fix has been running locally via patch-package against an 841-story production sweep with 0 ArgsProvider errors and 0 navigation errors before this PR was filed.

Change

packages/ladle/lib/app/src/compose-enhancers.tsx: when module[storyName] is an object, resolve a real component before passing it to ArgsProvider:

1. If storyExport.render is a function, wrap it as (props) => render(props) so createElement receives a function.
2. Else if the meta has a .component, render meta.component with the merged args (covers CSF v3 args-only and empty stories).
3. Else, fall back to a thin no-op renderer (defensive; not exercised by the production codebase).

CSF v2 stories (named-export-is-a-function) are unchanged — the typeof storyExport === "function" branch keeps the existing path.

Args / argTypes spread now walks storyExport.args / storyExport.argTypes (instead of relying on module[storyName].args); the new spread is symmetric for both shapes.

Test plan

• Existing tests pass (pnpm typecheck, pnpm lint, unit tests under packages/ladle, all e2e fixtures).
• New e2e/csf3 package with Playwright spec covering four CSF v3 shapes:
  • args-only (resolves to meta.component)
  • render-only (wraps renderFn)
  • render+args (renderFn receives merged args)
  • empty (defensive fallback / meta.component)
• Final assertion that none of those four CSF v3 stories logs an "Element type is invalid" error.
• CSF v2 fixtures in e2e/decorators continue to work (decorator chain, args, params, mock-date).

Out of scope

• Updating Ladle's exported Story<P> typing (currently extends React.FC<P>) to accept the object form. The runtime fix is sufficient for codebases that import StoryObj from @storybook/react; a follow-up PR can broaden Ladle's own type to match Storybook's StoryObj<…>.
• The TSSatisfiesExpression parser unwrap for named-identifier default exports (separate PR).