content: content/sanitize — drop invalid blocks tree-wide (799/799)

Enforcement counterpart to validate: removes blocks failing validate's own
per-block id/field checks (reused via content/-block-issues, single-sourced)
so federated/imported input can render safely. Tree-wide; distinct from
normalize (empty vs invalid); keeps valid-shell sections, drops invalid ones.
New suite +12 tests (42 suites total).

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

lib/content/scoreboard.json

@@ -31,6 +31,7 @@
     "data": {"pass": 25, "fail": 0},
     "wire": {"pass": 11, "fail": 0},
     "validate": {"pass": 32, "fail": 0},
+    "sanitize": {"pass": 12, "fail": 0},
     "store": {"pass": 46, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
@@ -42,7 +43,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 787,
+  "total_pass": 799,
   "total_fail": 0,
-  "total": 787
+  "total": 799
 }