fix(docs): make gen_ref_pages actually run under mkdocs-gen-files

[livingstaccato]

The API reference generator has never executed, in any invocation path. Every project that inherits this docs setup has been publishing a reference section containing one hand-written index page.

Under the plugin

mkdocs-gen-files runs a configured script with runpy.run_path(file_name) and no run_name (mkdocs_gen_files/plugin.py:43), so __name__ is "<run_path>". The entry point sat behind if __name__ == "__main__", which therefore never fired — the file defined its functions and returned.

The plugin cannot distinguish a script that generated nothing from one that had nothing to generate, so this failed silently. Downstream it shows up as dangling links out of the hand-written docs/reference/index.md, which looks like a docs-authoring problem and isn't.

Measured on provide-foundation:

	pages	mkdocs warnings
before	1	91
after	353	9

The 9 remaining are genuine griffe complaints about that project's own docstrings, fixed separately.

Under direct execution

Also broken, differently. The guard sat above the helpers generate_reference_pages() calls:

$ python gen_ref_pages.py
NameError: name '_resolve_src_root' is not defined

That's why the call has to be the last statement in the file, not merely unconditional.

Why __spec__ and not a bare call

provide.foundry.docs re-exports generate_reference_pages (docs/__init__.py:8), so a bare module-level call would write files as an import side effect. runpy.run_path and python gen_ref_pages.py both leave __spec__ as None; a genuine import sets it. That is exactly the distinction needed.

scripts/gen_monorepo_ref_pages.py:174 already calls its entry point unconditionally at module level — this brings the per-project script into line with the variant that works.

Verified

• import provide.foundry.docs — no generation, __spec__ is set
• python gen_ref_pages.py — reaches generation instead of raising
• plugin path — covered by the consuming provide-foundation build
• ruff check, ruff format, mypy strict all clean