fix(ci): pass --configpath to lua-language-server

Problem: lua-language-server --check lua/ treats lua/ as its workspace
root and fails to find .luarc.json in the project root, so diagnostics
globals (vim, jit) are not loaded and every vim.* reference is flagged
as undefined-global.

Solution: pass --configpath .luarc.json explicitly, matching what the
GitHub CI action already does.

scripts/ci.sh

@@ -6,5 +6,5 @@ git ls-files '*.lua' | xargs nix develop --command selene --display-style quiet
 nix develop --command prettier --check .
 nix fmt
 git diff --exit-code -- '*.nix'
-nix develop --command lua-language-server --check lua/ --checklevel=Warning
+nix develop --command lua-language-server --check lua/ --configpath .luarc.json --checklevel=Warning
 nix develop --command busted