Install atuin from upstream's binary; drop three uv tools

Install atuin from upstream's binary; drop three uv tools atuin returns to Nix, but not from nixpkgs. 18.21.0 requires rustc 1.98.0 and no nixpkgs revision has it - the locked input and master are both on 1.97.1 - so a source build fails outright. That is why nixpkgs is still on 18.19.0, and 18.19 cannot open a history database that 18.21 has migrated. nix/packages/atuin.nix packages the same prebuilt darwin binary mise was downloading, which sidesteps the compiler entirely. Verified: 18.21.0, same upstream commit, opens the existing 33 MB database. mise's global [tools] is empty again. The trade-off is a pinned hash to bump by hand on each release, where mise resolved "latest" on its own. The file documents the bump command and says to delete it once nixpkgs carries rustc >= 1.98.0. Also drops spec-kitty-cli, weasyprint and hypothesis, leaving uv-tools.sh with four: llvd and semble are absent from nixpkgs, grip and radon exist only as python3Packages.