Text angle support

Currently, the `text` method has `$angle` hardcoded at `0`, but angles are supported by the appropriate PHP functions.

The biggest challenge here is calculating the post-angle position of the text box and ensuring it gets positioned correctly based on `anchor`.

- [ ] Add `angle` to `$options`
- [ ] Keep between -360 and 360 degrees
- [ ] Make sure positioning works as expected (e.g. `top left` should still be in the top left corner at any angle)
- [ ] Document in the source comments
- [ ] Document in README.md

Start by locating the `text` method and its `$options` handling, then review the PHP image functions it uses and the existing anchor-positioning logic. Implementing this requires supporting angles from -360 to 360 degrees while preserving anchor placement, then documenting the option in the source comments and README.md. Done means rotated text is positioned correctly for anchors such as `top left`.

Written by the indexing model from the issue text.