cmd/hakurei: rename app to run

The run command was a legacy holdover from very early days and is only useful for testing and demonstration these days. This change also renames it to exec.

Signed-off-by: Ophestra <cat@gensokyo.uk>

test/sandbox/configuration.nix

@@ -30,7 +30,7 @@ in
 
       # For checking pd outcome:
       (pkgs.writeShellScriptBin "check-sandbox-pd" ''
-        hakurei -v run hakurei-test \
+        hakurei -v exec hakurei-test \
           -p "/var/tmp/.hakurei-check-ok.0" \
           -t ${toString (builtins.toFile "hakurei-pd-want.json" (builtins.toJSON testCases.pd.want))} \
           -s ${testCases.pd.expectedFilter.${pkgs.stdenv.hostPlatform.system}} "$@"