Build tooling work, commits C31-C50, C32a, C41a-c.

[KubaO]

• lib: the new top-level lib/markdown.mjs says which lines and spans of a markdown page are code, and lib/frontmatter.mjs parses a page's frontmatter. check_code_regions carries probes for both.
• builder: the pre-render rewrites and the admonition plugin find code through lib/markdown.mjs. So do counts.mjs, convert_em_dash_separators, check_examples' marker splice, check_gate_lists, and eval/'s run_case and nav_hops. nav_hops no longer misreads the fences in Authoring.md.
• builder: an unknown {{tbdocs:name}} count is reported with its file and line, and a name inside code is no longer checked.
• builder: gray-matter is removed. Frontmatter is read through lib/frontmatter.mjs everywhere: discover, eval/ and Wisdom.
• docs: the titles Input #, Line Input # and Write # are now quoted. Unquoted, YAML read the # as a comment, so the sidebar showed Input, Line Input and Write. The build now warns about any unquoted frontmatter value that ends in #.
• BETA 987: builder/package-api.json is regenerated. VB has two new private UDTs, _Collection lists its members in another order, and OrientationConstants moved into WinNativeCommonCtls' new public module Miscellaneous2. Add-in test P5 accepts the empty hover 987 gives where 983 gave none. examples.bat (1129 of 1129 samples compile) and addin-test.bat (10 of 10 lanes) pass on 987.
• wisdom: parseStaging splits only at real section boundaries, so a --- inside a fenced sample no longer ends a section. Pages and threads are read through lib/. Reference pages are grouped by package again: after the folder reorganisation they were grouped under Default and Built-In only.
• scripts: census_attributes and gen_attribute_probes share one reader of Attributes.md, scripts/lib/attributes-doc.mjs. Both now need npm install.
• scripts: check_links.mjs runs the build's own link and integrity checks (builder/check.mjs) over a tree on disk. Its report is unchanged.
• scripts: shared helpers replace copies:
  • scripts/lib/gate-probes.mjs holds the gates' probes and crash handler.
  • The two diagram tools share one browser launch and one Inter host page, and no longer pass --allow-file-access-from-files.
  • The a11y sampler and sweep share one page discovery.
  • lib/repo-paths.mjs gives 26 files one repository root.
• cli: lib/cli.mjs is built on node:util's parseArgs, and every tool under scripts/ now reads its command line through it, keeping its behaviour. The differences, all recorded in the plan:
  • --name=value is accepted.
  • A repeated flag keeps its last value.
  • -- ends the options.
  • A short-option group such as -vh is split into its letters.
  • survey_tooling's parse errors use the module's wording.
• test.bat: the new check_cli gate tests the module and 106 recorded command-line cases across 21 tools, each run with an IDE and a browser that do not exist. It is in test.bat and the shared CI action, so this is its first run on Linux.
• WIP.md: the file-editing tools turn a four-digit \u escape into the character itself. WIP.md now says so, and says to write the brace form \u{FEFF} instead.
• Docs (Tools.md, Building.md, Extending.md, Pipeline-Stages.md) and the WIP notes are updated to match. build.bat, check.bat, test.bat and lint are clean on every commit.