feat(ui): update frontend for direct DB insert — i18n, api client, components, models

- api.ts, api/translate.ts: add connection API methods (fetchConnections,
  createConnection, testConnection, etc.)
- i18n (en/ru): add connection management and insert method translation keys
- TranslationJobModel.svelte.ts: add insert_method, connection_id fields
- ConfigTabForm.svelte, RunTabContent.svelte: integrate InsertMethodSelector
- TranslationPreview.svelte, TranslationRunResult.svelte: show insert method
  badge and connection name in results
- TargetTabForm.svelte, TargetSchemaHint.svelte: insert method awareness
- routes.ts, routes-link-integrity: register connections settings tab
- test_translation_preview.svelte.js: update preview tests
- package.json: update deps as needed

frontend/package.json

@@ -39,8 +39,8 @@
   },
   "dependencies": {
     "@gradio/client": "^1.0.0",
+    "@humanspeak/svelte-markdown": "^1.6.0",
     "date-fns": "^4.1.0",
-    "diff2html": "^3.4.56",
-    "svelte-markdown": "^0.4.1"
+    "diff2html": "^3.4.56"
   }
 }