Remove treefmt and djlint from pre-commit hooks. djlint corrupted
Askama template syntax on first run. Use individual formatters
(cargo fmt, shfmt, oxfmt) directly instead. Update prek hooks
to use fmt-rs and fmt-sh separately.
Replace Nix flake with mise for toolchain management, treefmt for
formatting, prek for pre-commit hooks, and a Dockerfile for container
builds. Update CI workflows to use jdx/mise-action instead of Nix.
Add system dependency instructions to README.md and CLAUDE.md.
