Translate the connector page (DE, IT) - #1325

Summary

Fifth area of #1271, first half: the connector page (/connectors/[id]) in German and Italian, without its tools section. No behaviour changes, and Accept-Language: en-US renders exactly what it rendered before.

Splitting the area: like Connectors, connector detail is two PRs. The page is about 2,400 lines and the tool editor another 1,600, so together they would be over 4,000 lines. Both are under #1271 and come one at a time:

1. This PR: the page itself, without the tools section.
2. Next: the tools section (import panel, tool list, playground) with components/tool-editor/* and components/tool-annotations-editor.tsx.

Changes

• app/connectors/[id]/page.tsx:
  • the header actions (Test, Edit/Cancel, Export as JSON/YAML, Delete) and the delete dialog (both variants);
  • the status pill and the message box;
  • the test-result prefixes and the SSRF allowlist link;
  • the catalog update card;
  • the Connector Details card, in view mode and in edit mode for every auth type: API key, bearer, basic, WS-Security, OAuth 2.0 (grants, token endpoint auth, PKCE), OAuth 1.0a and login → token. Also the database access mode, denied tables, the OData/SAP fields, the healthcheck path and the instructions;
  • the OAuth2 and Shopee authorization cards;
  • the environment variables card;
  • the danger zone;
  • the page's own messages: OAuth callback results, auth validation errors, export, spec import, catalog update, environment variables saved, authorization and discovery failures.
• components/user-credentials-card.tsx: the shared or per-user sign-in card and its confirmation dialog. It's used only on this page.
• messages/{en,de,it}.json: new namespaces connectorDetail and userCredentials, with 191 keys each.
• Auth type label: the view mode now uses useAuthTypeLabel from Translate the connector list and marketplace (DE, IT) #1303, so it matches the connector cards.
• Dates: "Created" and "connected since" now follow the UI language instead of the browser's. For en-US they're unchanged.

Left in English on purpose:

• Text from the server and the catalog: error messages, warnings, the adapter's Markdown instructions, health and test messages.
• Technical names: Client ID, Client Secret, Token URL, Scopes, Bearer Token, Consumer Key/Secret, WS-Security, PasswordText/PasswordDigest, OAuth 1.0a, sap-client, POST/GET, and the example values in placeholders.
• The tools section and its messages (HAR import, tool created/updated, tool toggles), for the next PR.

Self-hosted vs Cloud: frontend only, with no backend, database or ee/ change.

Translations

German and Italian aren't my native languages, so please review those strings. I kept the tone and terms from the earlier PRs: German with Sie, Italian with tu, "Connector" / "connettore", "KI-Client" / "client AI", "API-Schlüssel" / "Chiave API". Strings I'm least sure about:

• The healthcheck hint: it names our own Test button, so it says „Testen“ / "Testa" where English says "Test connection".
• Catalog update list labels: "Aktualisiert / Neu / Deaktiviert" and "Aggiornati / Nuovi / Disattivati", and "Ihre eigenen, bleiben unverändert" / "I tuoi, lasciati come sono".
• "Leave empty to keep current": shortened to "Leer lassen zum Beibehalten" / "Lascia vuoto per mantenerlo" so it fits the half-width credential fields.
• The OAuth grant names: kept mostly as the OAuth terms, as in Translate the connector setup and new connector pages (DE, IT) #1318.
• "Gesperrte Tabellen" / "Tabelle bloccate" for "Denied tables".

	German	Italian
Header
Edit mode
Environment variables and danger zone

Type

• New feature

Testing

3 new tests in tests/e2e/i18n.spec.ts, with a mocked REST connector using an API key:

• de-DE: the page renders in German in view mode, the environment variables editor, edit mode (labels and the "keep current" placeholder), the danger zone and the delete dialog.
• it-IT: the page renders in Italian, including edit mode and the danger zone.
• en-US: everything stays exactly as before, including the delete dialog text.

The key-parity test from #1248 covers the new keys. The existing specs for this page (environment variables, OAuth grant and completion, OAuth 1.0a editing, export/import, catalog update preview) all still pass. I measured the page at 1280 px in German, Italian and English, and none of them overflows.

The backend isn't touched, so I didn't rerun its suite.

• Added/updated tests
• Tested manually. I checked the page in German and Italian in the browser with mocked API data (the screenshots above), not against a live backend.

Checklist

• My code follows the existing code style
• I have tested my changes locally
• I have updated documentation (if applicable). Not needed: CONTRIBUTING's "Translating the UI" section already covers new namespaces.
• All existing tests pass (frontend; backend unchanged)
• This PR has a descriptive title

packages/frontend/AGENTS.md and next-env.d.ts were rewritten by next dev locally and are left out, as AGENTS.md asks.

Related Issues

Part of #1271 (Connector detail, first half)