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.md

@@ -7,7 +7,7 @@ _Generated by `lib/content/conformance.sh`_
 | block | 38 | 0 | 38 |
 | doc | 40 | 0 | 40 |
 | render | 42 | 0 | 42 |
-| api | 26 | 0 | 26 |
+| api | 32 | 0 | 32 |
 | meta | 27 | 0 | 27 |
 | page | 7 | 0 | 7 |
 | page-full | 4 | 0 | 4 |
@@ -45,4 +45,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **772** | **0** | **772** |
+| **Total** | **778** | **0** | **778** |