The markdown extractor's docstring promised a heading --references--> node edge
when a backtick Name matches a known pattern, but nothing implemented it, so an
AST build produced no document-to-code edge at all.
extract_markdown now collects inline code spans outside fences and frontmatter as
raw_calls tagged language "markdown", owned by the heading they sit under (the
page before the first heading). A new markdown_mentions language resolver runs
after the id-remap passes and turns them into references edges: the explicit
path::Symbol[::member] form resolves through the cited file's symbols and is
EXTRACTED 1.0; a bare or dotted name resolves only when exactly one callable code
node carries that label and is INFERRED 0.95. Ambiguous names, builtins, missing
files and non-callable matches emit nothing. The shared cross-file call pass
skips markdown raw_calls so prose never emits calls edges.
Tests cover span classification, raw_call ownership, end-to-end resolution,
ambiguity, and cache round-tripping.
(cherry picked from commit 2d833a0a3c)
