lua: standardize indentation on tabs

[cpunt]

Summary

• normalize first-party Lua source, test, example, and tooling indentation to tabs
• configure EditorConfig and VS Code to insert four-column tabs for Lua
• add a syntax-aware make check-indent lint gate that preserves multiline string and comment payloads

Closes #195

Testing

• make check-indent — 515 Lua files pass
• make test — 1,125 tests pass
• luacheck tools tests/unit/tools/lua_indentation_spec.lua — 0 warnings and 0 errors

Notes

• make lint reaches Luacheck after the new indentation check passes, but remains non-zero on 1,180 pre-existing warnings (0 errors). The new tooling is warning-free.

[cpunt]

Closing as a duplicate of #321; both PRs point to the same branch and commit.