chore: fix build break (#483)

* fix(sling_test): update test for cook dir change

The cook command no longer needs database context and runs from cwd,
not the target rig directory. Update test to match this behavior
change from bd2a5ab5.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix(tests): skip tests requiring missing binaries, handle --allow-stale

- Add skipIfAgentBinaryMissing helper to skip tests when codex/gemini
  binaries aren't available in the test environment
- Update rig manager test stub to handle --allow-stale flag

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: julianknutsen <julianknutsen@users.noreply.github>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/sling_test.go

@@ -328,9 +328,7 @@ exit 0
 		switch {
 		case strings.Contains(args, " cook "):
 			gotCook = true
-			if dir != wantDir {
-				t.Fatalf("bd cook ran in %q, want %q (args: %q)", dir, wantDir, args)
-			}
+			// cook doesn't need database context, runs from cwd
 		case strings.Contains(args, " mol wisp "):
 			gotWisp = true
 			if dir != wantDir {