docs(code-languages): add Lua and GSC skills

Lua covers dialect pinning (5.1/LuaJIT/5.2/5.3+/HavokScript), luac -p and
luacheck as the only real gate for an embedded host, locals over globals,
pcall at the boundary, the #t / pairs / pattern traps, and the sandboxed-host
rules including Call of Duty LUI specifics.

GSC covers the absence of any compiler, linter, or test harness and what to
do instead, scope prefixing on level/self, isdefined on every external read,
endon before the first wait, the per-frame instruction budget, load-phase
precaching, and side effects on shared level state.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -24,6 +24,8 @@ A collection of public, reusable agent skills, cheatsheets, and operational work
 | **Go** | [`go.md`](skills-public/code-languages/go.md) | strict `golangci-lint` set, concrete types over `interface{}`, context everywhere, CGO-free static builds |
 | **C# / .NET** | [`csharp-dotnet.md`](skills-public/code-languages/csharp-dotnet.md) | `TreatWarningsAsErrors`, nullable enabled, no `.Result`, trimming/single-file publish caveats, SDK shims |
 | **C / C++** | [`c-cpp.md`](skills-public/code-languages/c-cpp.md) | full warning set + `-Werror`, sanitizers, RAII/Rule of Zero, target-based CMake, FFI ownership |
+| **Lua** | [`lua.md`](skills-public/code-languages/lua.md) | pin the dialect first, `luac -p` + luacheck as the only gate, locals over globals, `pcall` at the boundary, `#t`/pattern traps, embedded & HavokScript hosts |
+| **GSC** | [`gsc.md`](skills-public/code-languages/gsc.md) | no compiler or test harness, `isdefined` on everything external, `endon` before the first wait, per-frame budget, precache at load, level-state side effects |
 
 Each language file extends `coding-dev.md` rather than repeating it. A project's own
 `AGENTS.md` / `CLAUDE.md` / `.rules` always overrides both.