content: validation vets list items + table cells element-deep (787/787)

validate only checked that list items / table rows-headers ARE lists; a
non-string item or non-list/non-string-cell row passed yet crashes asText/
render/find-replace/search. Added ct-all-str?/ct-all-rows? + deepened list/
table branches (guarded against double-reporting). +9 validate tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/content/scoreboard.json

@@ -30,7 +30,7 @@
     "media": {"pass": 15, "fail": 0},
     "data": {"pass": 25, "fail": 0},
     "wire": {"pass": 11, "fail": 0},
-    "validate": {"pass": 23, "fail": 0},
+    "validate": {"pass": 32, "fail": 0},
     "store": {"pass": 46, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
@@ -42,7 +42,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 778,
+  "total_pass": 787,
   "total_fail": 0,
-  "total": 778
+  "total": 787
 }