content: tree-wide content/find + has? (778/778)

Facade read-by-id was top-level only while content/edit's update/delete are
tree-wide — could not read back a nested block content/edit just modified.
Added generic ct-find-id (doc.sx) + doc-find-deep/doc-has-deep?; content/find
+ has? now descend into sections. content/find-top/has-top? keep top-level
lookup. Audit: remaining doc-find/ct-index-of callers are positional
insert/move (top-level by design). +6 api tests.

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

lib/content/scoreboard.json

@@ -3,7 +3,7 @@
     "block": {"pass": 38, "fail": 0},
     "doc": {"pass": 40, "fail": 0},
     "render": {"pass": 42, "fail": 0},
-    "api": {"pass": 26, "fail": 0},
+    "api": {"pass": 32, "fail": 0},
     "meta": {"pass": 27, "fail": 0},
     "page": {"pass": 7, "fail": 0},
     "page-full": {"pass": 4, "fail": 0},
@@ -42,7 +42,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 772,
+  "total_pass": 778,
   "total_fail": 0,
-  "total": 772
+  "total": 778
 }