When building the legacy config compat layer, namespace mappings like
`fontSize` → `text`, `boxShadow` → `shadow`, `animation` → `animate`,
etc. spread the result of `theme(namespace, {})` directly:
```ts
...(theme('text', {}) ?? {})
```
Some of these namespaces can return a **string** (e.g. `theme('text',
{})` → `'1rem'`). Spreading a string produces char-indexed keys (`{ '0':
'1', '1': 'r', ... }`) instead of a `{ DEFAULT: ... }` entry, silently
corrupting the compat config output.
This PR adds a small `spreadTheme` helper that normalizes the return
value before spreading:
- `string` → `{ DEFAULT: value }`
- plain object → `{ ...value }`
- anything else → `{}`
and updates all namespace mappings to use it. Includes unit tests for
the helper plus integration tests for the affected namespaces and the
string-return regression cases.
---------
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
16e94cbf7f