content: tree reparent — move-into section + promote (812/812)

insert/move were top-level only; a block could never move into/out of a
section. content/move-into (relocate to a section child at index, tree-wide)
+ content/promote (lift nested block to top level, subtree intact). Pure
tree transforms like the rest of move.sx; cycle-safe (rejects moving a block
into its own descendant). +13 tests.

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

lib/content/scoreboard.json

@@ -12,7 +12,7 @@
     "section": {"pass": 25, "fail": 0},
     "compose": {"pass": 17, "fail": 0},
     "tree-edit": {"pass": 17, "fail": 0},
-    "move": {"pass": 11, "fail": 0},
+    "move": {"pass": 24, "fail": 0},
     "clone": {"pass": 10, "fail": 0},
     "query": {"pass": 20, "fail": 0},
     "toc": {"pass": 8, "fail": 0},
@@ -43,7 +43,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 799,
+  "total_pass": 812,
   "total_fail": 0,
-  "total": 799
+  "total": 812
 }