feat: add .emmyrc.json for LuaJIT runtime and workspace config (#1505)

Add .emmyrc.json to configure EmmyLua with LuaJIT runtime and set
require patterns for Lua files. Also includes $VIMRUNTIME in the
workspace library for better Neovim integration.

Author: deathbeam

.emmyrc.json

@@ -0,0 +1,9 @@
+{
+  "runtime": {
+    "version": "LuaJIT",
+    "requirePattern": ["lua/?.lua", "lua/?/init.lua"]
+  },
+  "workspace": {
+    "library": ["$VIMRUNTIME"]
+  }
+}