chore(configs): migrate oxlint→eslint presets, refactor tsconfig

- Replace @robonen/oxlint with @robonen/eslint (composable ESLint flat-config
  presets: base, typescript, vue, vitest, imports, node, stylistic).
- Plugins bundled as deps: typescript-eslint, eslint-plugin-vue,
  @vitest/eslint-plugin, eslint-plugin-import-x, eslint-plugin-n,
  eslint-plugin-unicorn, @stylistic/eslint-plugin.
- @robonen/tsconfig: add base/dom/node/vue configs for composite project refs.

configs/eslint/src/compose.ts

@@ -0,0 +1,34 @@
+import type { FlatConfigArray, FlatConfigInput } from './types';
+
+/**
+ * Compose multiple ESLint flat configurations into a single flat config array.
+ *
+ * ESLint flat config is an ordered array where later entries override earlier
+ * ones, so composition is a flatten: each preset (an array) and each inline
+ * override (a single object) are concatenated in order. `undefined`/`null`
+ * inputs are skipped, allowing conditional spreads.
+ *
+ * @example
+ * ```ts
+ * import { compose, base, typescript, vue } from '@robonen/eslint';
+ *
+ * export default compose(base, typescript, vue, {
+ *   rules: { 'no-console': 'off' },
+ * });
+ * ```
+ */
+export function compose(...configs: Array<FlatConfigInput | false | null | undefined>): FlatConfigArray {
+  const result: FlatConfigArray = [];
+
+  for (const config of configs) {
+    if (!config)
+      continue;
+
+    if (Array.isArray(config))
+      result.push(...config);
+    else
+      result.push(config);
+  }
+
+  return result;
+}