ci(make): reserve exit 69 for "could not run" (D-26)

Environment guards now exit 69 rather than 1, so a caller can tell a suite
that could not start from one that ran and failed. The first toj test sweep
reported "3 repositories failed" and none of the three had executed a test —
two could not find go, one had no venv. That points the reader at the tests
when the fault is in the environment.

Only the environment guards change. A gitleaks finding, a failed test run and
a vulncheck hit still exit 1, because those did run and did fail.

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

Makefile

@@ -24,7 +24,7 @@ generate: ## Regenerate freezed/json_serializable/riverpod sources
 .PHONY: test
 test: ## Run the widget and unit tests
 	@test -f lib/core/auth/user_preferences.freezed.dart \
-	  || { echo "FAIL — generated sources missing; run: make setup"; exit 1; }
+	  || { echo "FAIL — generated sources missing; run: make setup"; exit 69; }
 	flutter test
 
 # Why the guard above: *.freezed.dart and lib/**/*.g.dart are gitignored, so a