fix(pages): stop Jekyll dropping _shared.lua from the published site

Irish transcription is broken in production with a 404 on
wiktionary_pron/lua_modules/ga-passes/_shared.lua.

The Pages build runs actions/jekyll-build-pages (see
.github/workflows/jekyll-gh-pages.yml), and Jekyll excludes any path whose
basename begins with an underscore. The file is committed and correct, but it
never reaches the built site. Confirmed against production: in the same
directory and commit, 01_polarity.lua returns 200 while _shared.lua returns
404 — the only difference is the leading underscore.

This breaks Irish completely: all 17 passes plus the engine require the module,
so the first fetch fails and nothing transcribes.

Adding _config.yml with an explicit `include` puts the file back in the build
output. Note that a .nojekyll file would NOT help here: that only bypasses the
legacy Pages pipeline, not an explicit jekyll-build-pages run.

Chose this over renaming the file to shared.lua, which would have touched 19
call sites and broken the byte-identical invariant with the source repo
(wiktionary_ipa_phoneme_lexicons/irish/passes/), where the module is _shared.lua
and the sync is a mechanical passes. -> ga-passes. rewrite.

_shared.lua is currently the only underscore-prefixed tracked file in the repo.

Author: hellpanderrr

_config.yml

@@ -0,0 +1,16 @@
+# Jekyll configuration for GitHub Pages.
+#
+# This site is a plain static site — nothing here uses Jekyll's templating. The
+# only reason this file exists is that the Pages build (see
+# .github/workflows/jekyll-gh-pages.yml, which runs actions/jekyll-build-pages)
+# excludes any path whose basename starts with an underscore. That silently
+# dropped wiktionary_pron/lua_modules/ga-passes/_shared.lua from the published
+# site, giving a 404 and breaking Irish transcription entirely — every one of
+# the 17 Irish passes requires that module.
+#
+# `include` re-adds specific underscore-prefixed paths to the build output.
+include:
+  - wiktionary_pron/lua_modules/ga-passes/_shared.lua
+
+# Deliberately no `exclude:` list — Jekyll's defaults already skip node_modules
+# and .github, and overriding it here risks dropping something the site serves.