gem 0.1.0

Color representations and conversions

### Fixed

- **`cargo publish`'s own verification build failed**: `default = []` meant a bare `cargo add gem`
  (or `cargo publish`, which builds the default feature set to verify the package) failed to
  compile, because the always-compiled `space` module hits a `compile_error!` in `src/space/math.rs`
  without `std` or `libm` enabled. This shipped in the `v0.1.0` tag's first publish attempt, which
  failed in CI before anything reached crates.io. Fixed by making `default = ["libm"]`; consumers
  who only want zero-cost pixel formats can still `default-features = false`. Added `cargo build`
  (default features) to `just check` so this class of regression fails CI immediately instead of
  only surfacing at publish time.
- `named` module doc comment claimed "147" CSS named colors while only defining 141 `const`s.
  Added the 7 missing British-spelling aliases (`GREY`, `DARK_GREY`, `DARK_SLATE_GREY`,
  `DIM_GREY`, `LIGHT_GREY`, `LIGHT_SLATE_GREY`, `SLATE_GREY`) so the crate now defines all 148
  CSS Color Module Level 4 named colors, and corrected the doc count.

### Changed

- **License changed from `MIT` to `MIT OR Apache-2.0`**, matching every other crate in the
  ecosystem (`ixy`, `grixy`, `hexal`, `framepace`). Added `LICENSE-APACHE` and renamed `LICENSE` to
  `LICENSE-MIT`.
- **MSRV lowered from `1.88` to `1.87`**, matching the rest of the ecosystem. Verified the crate
  builds, lints, and tests clean on `1.87` with `--all-features`; nothing in the source actually
  required `1.88`.

### Chores

- `just semver-checks` no longer hardcodes a stale prerelease baseline (`0.1.0-alpha.4`); lets
  `cargo-semver-checks` auto-select the latest published baseline, matching `grixy`'s fix for the
  same issue.