chore(encoding): eslint/tsconfig migration

Migrate to eslint flat config (qr-code.ts override for the mask-penalty
sliding-window) and composite tsconfig.

core/encoding/eslint.config.ts

@@ -0,0 +1,13 @@
+import { base, compose, imports, stylistic, typescript } from '@robonen/eslint';
+
+export default compose(base, typescript, imports, stylistic, {
+  name: 'encoding/overrides',
+  files: ['src/qr/qr-code.ts'],
+  rules: {
+    '@stylistic/max-statements-per-line': 'off',
+    '@stylistic/no-mixed-operators': 'off',
+    /* Uniform sliding-window register shift (h6 = h5; h5 = h4; …) where the
+       oldest register's seed/last write is intentionally dead — keep symmetry. */
+    'no-useless-assignment': 'off',
+  },
+});