Gate each check behind staged file pattern matching so a docs
or backlog change no longer triggers the full test suite. Add
presto pytest and Docker image validation guards. Fall back to
running all checks when invoked directly (not via git commit).
Mix aliases should only compose mix tasks. Shell tool orchestration
(shellcheck, fd) belongs in mise scripts. This removes the mix cmd
escape hatch and makes the boundary clear: mix.exs for pure mix
composition, scripts/ for cross-toolchain orchestration.