Porting Makefile pattern rules to just: glob loop recipe

just has no pattern rules or up-to-date checks, so a make rule like out/%.pdf: src/%.typ becomes a private shebang recipe taking (pattern, outdir) that loops over an unquoted glob with shopt -s nullglob and derives the output name via basename "${f%.typ}". Dependency syntax like lectures: (_build-all "lec[0-9]*.typ" "lectures") reuses it per folder. Watch out: running the full recipe once rebuilds every tracked output and dirties git, so restore untouched outputs with git checkout. On NixOS without just installed, test with nix run nixpkgs#just -- <recipe>.