Update nvim config: switch to tab indentation, update claudecode and vimade settings

Remove stylua.toml (was enforcing 2-space indent), add tab settings in options.lua,
update claudecode.nvim terminal/diff config, lower vimade fadelevel to 0.6, remove
claudecode LazyExtra in favor of custom plugin spec, and add .luarc.json.

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

nvim/.luarc.json

@@ -0,0 +1,12 @@
+{
+  "runtime": {
+    "version": "LuaJIT"
+  },
+  "diagnostics": {
+    "globals": ["vim", "LazyVim", "Snacks"]
+  },
+  "workspace": {
+    "library": ["${3rd}/luv/library"],
+    "checkThirdParty": false
+  }
+}