🔧 Replace ESLint and Prettier with oxlint and oxfmt

- Drop .eslintrc.cjs and .prettierrc, add .oxlintrc.json and .oxfmtrc.json
- oxlint covers correctness/suspicious/perf/style/restriction categories
  plus import and typescript plugins; oxfmt reads the same .prettierrc-style
  options we had before
- Update lefthook.yml pre-commit jobs to run oxlint/oxfmt instead of
  eslint/prettier
- Update .vscode/extensions.json (oxc replaces eslint/prettier/vitest) and
  settings.json (oxc becomes the default formatter for TS/JS)
- Add 'oxlint', 'oxfmt', 'oxc', 'nodenext' to cspell dictionary
- Rewrite README 'Development' section to describe the new toolchain

.vscode/settings.json

@@ -1,7 +1,11 @@
 {
     "typescript.tsdk": "node_modules/typescript/lib",
     "[typescript]": {
-        "editor.defaultFormatter": "esbenp.prettier-vscode",
+        "editor.defaultFormatter": "oxc.oxc-vscode",
+        "editor.formatOnSave": true
+    },
+    "[javascript]": {
+        "editor.defaultFormatter": "oxc.oxc-vscode",
         "editor.formatOnSave": true
     },
     "[json]": {
@@ -12,10 +16,6 @@
         "editor.defaultFormatter": "esbenp.prettier-vscode",
         "editor.formatOnSave": true
     },
-    "editor.defaultFormatter": "esbenp.prettier-vscode",
-    "editor.formatOnSave": true,
-    "[javascript]": {
-        "editor.defaultFormatter": "esbenp.prettier-vscode",
-        "editor.formatOnSave": true
-    }
-}
+    "editor.defaultFormatter": "oxc.oxc-vscode",
+    "editor.formatOnSave": true
+}