feat(linter): GL033 static dead-rules detection

Add rule GL033 that warns when every rule in a job's rules: block has
an explicit when: never, making the job permanently excluded from any
pipeline run. This is a pure static check — no if: evaluation or context
required. Only rules with literal when: never trigger it; rules with no
when: (defaults to on_success), when: manual, when: always, or
when: on_failure are treated as reachable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Taskfile.yml

@@ -81,6 +81,8 @@ tasks:
         ignore_error: false
       - cmd: ./{{.BINARY}} check testdata/variable_refs_included.yml
         ignore_error: false
+      - cmd: ./{{.BINARY}} check testdata/dead_rules.yml
+        ignore_error: false
       - cmd: ./{{.BINARY}} check testdata/samba/.gitlab-ci.yml
         ignore_error: false
       - cmd: ./{{.BINARY}} check testdata/samba/.gitlab-ci-coverage.yml