chore: add husky and lint-staged for pre-commit linting and type-checking (closes #404)

.husky/pre-commit

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+npx lint-staged

lint-staged.config.mjs

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+// lint-staged configuration.
+//
+// - ESLint --fix runs on staged JS/TS files (this project's linter/formatter; there is no Prettier).
+// - Type-checking runs `tsc --noEmit` across the whole project, NOT on individual staged files:
+//   passing filenames to tsc makes it ignore tsconfig.json (path aliases like `@/*`, jsx, strict
+//   options), which would fail on almost every commit. The function form below returns a single
+//   project-wide command and ignores the staged filenames lint-staged would otherwise append.
+export default {
+  "*.{js,jsx,ts,tsx}": "eslint --fix",
+  "*.{ts,tsx}": () => "tsc --noEmit",
+};