fix(pipeline-doctor): add gawk to runtimeInputs (#1)

writeShellApplication restricts PATH to runtimeInputs, which omitted gawk.
The token-leak check's line-continuation flattening shells out to awk, so the
doctor crashed with 'awk: command not found' (exit 127) in minimal Nix runtimes
(e.g. the nixos/nix CI image), aborting downstream build/publish in consumer
pipelines. Add gawk so awk resolves.

Verified: nix build .#pipeline-doctor then run against a repo -> 9 passed,
0 failed, exit 0.

flake.nix

@@ -58,6 +58,7 @@
             coreutils
             gnugrep
             gnused
+            gawk
             findutils
             jq
           ];