refactor(level): four essential rungs only — integration & recipe-local are optional

Per operator: the level ladder is now the FOUR essential rungs every recipe is
held to — install, upgrade (essential), backup/restore, functional (top = L4).
Integration (SSO/OIDC) and recipe-local are OPTIONAL capabilities: they no longer
appear as level rungs or skip rows and never cap the level. SSO is still enforced
for the run VERDICT (unchanged in run_recipe_ci.py); it just doesn't affect the
level. derive_rungs simplified accordingly (drops declared/deps/sso/repo-local
inputs). custom-html-tiny's EXPECTED_NA is back to just backup_restore.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_dashboard.py

@@ -24,7 +24,7 @@ import dashboard  # noqa: E402
 def _row(**kw):
     base = {
         "recipe": "custom-html", "status": "success", "number": 4, "ref": "db9a9502",
-        "version": "db9a95024e9d", "level": 4, "level_cap_reason": "L5 integration N/A",
+        "version": "db9a95024e9d", "level": 4, "level_cap_reason": "",
         "has_screenshot": True, "flags": {"clean_teardown": True, "no_secret_leak": True},
         "finished": 0, "url": "https://drone.x/cc-ci/4",
     }