docs(claude): add Lua path-scoped rules

Author: mimikun

dot_claude/rules/lua.md

@@ -0,0 +1,12 @@
+---
+paths:
+  - "**/*.lua"
+---
+
+# Lua
+
+- **Formatter:** `stylua` — 2-space indent, double quotes, always parenthesize calls (`require("x")`)
+- **Linter:** `selene`
+- **Pre-commit checks:** `stylua --check . && selene .`
+- Target **Lua 5.1 / LuaJIT** — NEVER use Lua 5.3+ syntax (bitwise `&`/`|`/`~`, integer division `//`); use the `bit` library
+- **Neovim configs:** prefer `vim.opt.*` / `vim.api.*` over legacy vimscript; guard optional `require()` with `pcall`