content: video/audio media block (media.sx) + 15 tests (683/683)

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

lib/content/scoreboard.json

@@ -25,6 +25,7 @@
     "stats": {"pass": 17, "fail": 0},
     "table": {"pass": 15, "fail": 0},
     "callout": {"pass": 12, "fail": 0},
+    "media": {"pass": 15, "fail": 0},
     "data": {"pass": 21, "fail": 0},
     "wire": {"pass": 11, "fail": 0},
     "validate": {"pass": 23, "fail": 0},
@@ -37,7 +38,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 668,
+  "total_pass": 683,
   "total_fail": 0,
-  "total": 668
+  "total": 683
 }