🗑️ chore: remove outdated instructions and migration documentation

frontend/AGENTS.md

@@ -0,0 +1,37 @@
+# Frontend
+
+Svelte 5 SPA bundled with esbuild and styled with Tailwind CSS 4.
+
+## Structure
+
+- Entry point: `src/index.ts`, main component: `src/App.svelte`.
+- `src/lib/` — utilities, stores, actions, API layer.
+- `src/widgets/` — reusable UI components (Button, Input, Form, etc.).
+- `src/css/` — global styles and Tailwind imports.
+- Keep route components in a `src/routes/` folder when needed.
+
+## Conventions
+
+- PascalCase component names; export props at the top of `<script>` tag.
+- Keep code and comments in English.
+- SSR safety: guard browser-only code with `typeof window !== "undefined"`.
+- API behavior: PUT responses return only changed fields; filter by id uses `_id`; API requests reject non-2xx with `{ response, data }` and error payload in `error.data.error`.
+
+## Tailwind CSS
+
+- Always use canonical Tailwind utility classes instead of arbitrary values when a standard equivalent exists (e.g. `h-16.5` not `h-[66px]`, `min-h-3` not `min-h-[12px]`).
+- Only use arbitrary values (`[...]`) when no standard utility covers the needed value.
+
+## i18n
+
+- `svelte-i18n` is configured in `src/lib/i18n/index.ts` with lazy loading for locale files.
+- Locale files live in `src/lib/i18n/locales/{lang}.json`.
+- URL-based language routing: `/{lang}/...` (e.g. `/de/`, `/en/about`).
+- Language utilities in `src/lib/i18n.ts`: `extractLanguageFromPath()`, `localizedPath()`, `getLanguageSwitchUrl()`.
+- Use `$_("key")` from `svelte-i18n` for translations in components.
+
+## Related tests
+
+- When developing frontend features: extend or create corresponding E2E tests in `tests/e2e/`.
+- After frontend changes, run only the affected E2E tests: `npx playwright test tests/e2e/filename.spec.ts` or `-g "test name"`.
+- When tests fail, clarify whether the frontend or the test needs adjustment — coordinate with the user.