gem 0.1.0-alpha.5

Color representations and conversions

### Added

- **Color spaces**: `Srgb`, `LinearRgb`, `Hsl`, `Hsv`, `Oklab`, `Oklch`  per-channel `f32` types with `From` conversions between all spaces.
  `Oklch` requires the `std` or `libm` feature for trigonometric functions.
- **Blending**: `alpha_over`, `premultiply`, `unpremultiply`, `lerp`
  functions in the new optional `blend` module (gated behind `features = ["blend"]`).
  Compatible with the standalone `alpha-blend` crate for full Porter-Duff compositing.
- **Named colors**: All ~147 CSS named color constants in the `named` module.
- **Conversions**: Pixel format types (`Rgb888`, `Bgr888`, `Abgr8888`,
  `Argb8888`) can now convert to/from `Srgb`.
- `From<u32>` / `From<Self> for u32` for packed integer types.
- `Hash` derive on all integer-component pixel format types.
- `UpperHex`, `LowerHex`, `Display` impls for integer formats.
- `From<[u8; N]>` / `From<T> for [u8; N]` for `Rgb888`, `Bgr888`.
- `std` and `libm` feature flags for float math support in `no_std`
  environments (follows the `alpha-blend` pattern).

### Changed

- **New lint configuration**: now matches `rg``unsafe_code = "deny"`,
  `clippy::all`, `pedantic`, and `nursery` all denied.
- `AlphaFirst` and `AlphaLast` docs clarified to show memory-order
  vs. constructor argument order.
- Fixed nightly-only doc attribute.
- Updated README to show correct API (`from_abgr` instead of `new_red`).