test(#1496): add behavioral validateCapability check for capability tutorial manifests (#1497)

* test(#1464): add behavioral manifest-validation test for capability tutorial docs

Extracts JSON capability manifests from tutorial/reference docs and validates
them through the real validateCapability — closing the test gap that let
issue #1464's broken tutorial manifest (step missing ref) pass undetected.

Adds fix-1464-docs-manifest-validation.test.cjs with:
- Suite 1: build/install/reference docs' complete manifests pass validateCapability
- Suite 2: adversarial fixtures prove the original #1464 bug shapes are caught
  (step without ref → "steps[0].ref must be an object…"; id/folderId mismatch)
- Suite 3: extractManifests helper unit tests (complete vs. partial block filtering)

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

* test(#1496): allowlist docs module for 3-file test cluster

docs-parity-live-registry, docs-update, and the new
fix-1464-docs-manifest-validation sit on the same docs production
module; add the docs entry to lint-test-file-count.allowlist.json
so the novel-offender CI gate passes.

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

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/lint-test-file-count.allowlist.json

@@ -175,6 +175,14 @@
         "external-job-waiting.test.cjs"
       ],
       "issue": "#1165"
+    },
+    "docs": {
+      "files": [
+        "docs-parity-live-registry.test.cjs",
+        "docs-update.test.cjs",
+        "fix-1464-docs-manifest-validation.test.cjs"
+      ],
+      "issue": "1496"
     }
   }
 }