refactor(frontend): migrate Svelte stores from .ts to .svelte.ts runes

- Delete legacy .ts stores (auth, activity, assistantChat, datasetReview, environmentContext, health, sidebar, taskDrawer, translationRun)
- Create new .svelte.ts runes-based stores using  reactive primitives
- Migrate i18n: /i18n → /i18n/index.svelte.js
- Migrate toasts: /toasts → /toasts.svelte.js
- Update all component imports across 180+ files: components, pages, routes, lib
- Remove fromStore() wrappers — use store.value directly with Svelte 5 runes
- Update test mocks for new import paths
- Add @DEPRECATED annotation to legacy  alias

frontend/src/components/storage/FileList.svelte

@@ -16,8 +16,8 @@
 <script lang="ts">
   // [SECTION: IMPORTS]
   import { downloadFile } from '../../services/storageService';
-  import { t } from '../../lib/i18n';
-  import { addToast } from '../../lib/toasts';
+  import { t } from '$lib/i18n/index.svelte.js';
+  import { addToast } from '$lib/toasts.svelte.js';
   // [/SECTION: IMPORTS]
 
   let {

frontend/src/components/storage/FileUpload.svelte

@@ -16,8 +16,8 @@
 <script lang="ts">
   // [SECTION: IMPORTS]
   import { uploadFile } from '../../services/storageService';
-  import { addToast } from '../../lib/toasts';
-  import { t } from '../../lib/i18n';
+  import { addToast } from '$lib/toasts.svelte.js';
+  import { t } from '$lib/i18n/index.svelte.js';
   // [/SECTION: IMPORTS]
 
   // #region handleUpload:Function [TYPE Function]