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/tests/api.sx

@@ -97,3 +97,37 @@
   "render original unchanged"
   (content/render d1 "html")
   "<h1>Hi</h1><p>World</p>")
+
+;; ── facade find/has? are TREE-WIDE (reach into sections); find-top/has-top?
+;; keep the top-level-only lookup. This makes the read-by-id surface consistent
+;; with content/edit, whose update/delete are already tree-wide. ──
+(content-bootstrap-section!)
+(define
+  nd
+  (content/append
+    (content/empty "nested")
+    (mk-section
+      "sec"
+      (list (content/block "text" "inner" (list (list "text" "deep")))))))
+(content-test
+  "find nested (deep)"
+  (blk-id (content/find nd "inner"))
+  "inner")
+(content-test "has? nested (deep)" (content/has? nd "inner") true)
+(content-test "find-top misses nested" (content/find-top nd "inner") nil)
+(content-test "has-top? misses nested" (content/has-top? nd "inner") false)
+(content-test
+  "find-top sees top-level"
+  (blk-id (content/find-top nd "sec"))
+  "sec")
+;; a nested block updated by id via content/edit is now readable by id via
+;; content/find (was impossible when find was top-level-only).
+(content-test
+  "edit-then-find nested round-trip"
+  (str
+    (blk-send
+      (content/find
+        (content/edit nd (content/update "inner" "text" "edited"))
+        "inner")
+      "text"))
+  "edited")