🔧 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

cspell.json

@@ -1,6 +1,15 @@
 {
     "version": "0.2",
     "language": "en",
-    "words": ["tslib", "typefest", "lefthook"],
+    "words": [
+        "tslib",
+        "typefest",
+        "lefthook",
+        "oxlint",
+        "oxfmt",
+        "oxc",
+        "nodenext",
+        "nocheck"
+    ],
     "ignorePaths": ["dist", "node_modules", "public", "coverage", "*.svg"]
-}
+}