content: content/block-path + block-depth — locate a block in the tree (825/825)

Read-side companion to doc-find-deep + reparent: ancestor-section chain
(root-first) for a block id, nil if absent (distinct from () top-level path);
block-depth is the path length. For breadcrumbs / scoping. New suite +13.
Probe this pass found no bugs: clone/remap tree-wide, all block types have
asMarkdown:.

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

lib/content/scoreboard.json

@@ -13,6 +13,7 @@
     "compose": {"pass": 17, "fail": 0},
     "tree-edit": {"pass": 17, "fail": 0},
     "move": {"pass": 24, "fail": 0},
+    "block-path": {"pass": 13, "fail": 0},
     "clone": {"pass": 10, "fail": 0},
     "query": {"pass": 20, "fail": 0},
     "toc": {"pass": 8, "fail": 0},
@@ -43,7 +44,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 812,
+  "total_pass": 825,
   "total_fail": 0,
-  "total": 812
+  "total": 825
 }