Lua 5.5 added a third 'seed' parameter to lua_newstate().
Use version check to pass the extra argument when needed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Wires mcpplibs.capi.lua into the mcpp build system. The descriptor:
- targets `capi-lua` (lib) at `src/capi/lua.cppm` (override the
  default lib-root convention which would look at `src/lua.cppm`),
- depends on the upstream Lua 5.4.7 C library shipped via
  mcpp-community/mcpp-index (added 2026-05-09).

mcpp 0.0.3's transitive walker propagates lua's headers into our
compile rule, so the existing `extern "C" { #include <lua.h> ... }`
in `src/capi/lua_headers.h` keeps working with no path tweaking.
Verified locally: `mcpp build` is clean against a fresh `target/`.

Replaces the multi-platform xmake CI with a single mcpp-driven
Linux job:
- `.xlings.json` declares `mcpp = { linux = "0.0.3" }`.
- `.github/workflows/ci.yml` boots xlings, runs `xlings install -y`,
  then `mcpp build` + `mcpp test` against the existing mcpp.toml.

xmake.lua + CMakeLists.txt stay untouched for local development; CI
on Linux now goes through mcpp end-to-end.

mcpp 0.0.3's binary lives at xim-x-mcpp/0.0.3/bin/mcpp; on first
run it self-detects home as that grandparent and bootstraps musl-gcc
+ binutils + glibc + ninja + patchelf into <home>/registry/data/xpkgs.
Toolchain set is version-pinned by mcpp 0.0.3, so a fixed cache key
is safe. Cache-hit runs skip the ~800 MB download.

* chore: migrate deps to namespace syntax (mcpp 0.0.6)

Updates mcpp.toml to use explicit namespace fields:
- [package].namespace added
- [package].name uses short name only
- [dependencies.compat] / [dev-dependencies.compat] for non-modular libs
- [dependencies.mcpplibs.capi] for C API wrappers

* ci: retrigger with fixed mcpp 0.0.6

lua (C library) and gtest are compat (non-modular) packages in
mcpp-index. Declare them under [dependencies.compat] /
[dev-dependencies.compat] subtables so mcpp resolves the correct
namespace ("compat") instead of the default ("mcpp") namespace.

Required for mcpp 0.0.10+ namespace-aware dependency pipeline.

- .xlings.json: mcpp 0.0.8 → 0.0.11
- CI: mcpp 0.0.11
- README: add mcpp build/usage section