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/api.sx

@@ -25,8 +25,13 @@
 (define content/append doc-append)
 (define content/blocks doc-blocks)
 (define content/count doc-count)
-(define content/find doc-find)
-(define content/has? doc-has?)
+;; find / has? are TREE-WIDE by id (descend into sections) — so the facade reads
+;; back any block content/edit can update or delete. content/find-top / has-top?
+;; keep the top-level-only lookup for callers that mean the ordered sequence.
+(define content/find doc-find-deep)
+(define content/has? doc-has-deep?)
+(define content/find-top doc-find)
+(define content/has-top? doc-has?)
 (define content/ids doc-ids)
 (define content/types doc-types)