fix(providers): complete OAuth logins that finish in the browser

OpenCode's authorize response reports how the client must finish: `code`
expects a pasted code, while `auto` requires the client to call
oauth/callback immediately and hold it open — upstream blocks in there
polling for the device code or waiting on its loopback redirect, and only
that call persists the credential. Every auth plugin OpenCode ships uses
`auto`; none use `code`.

The page implemented only `code`. It opened the browser, showed a paste
field no provider can fill, and never called back, so a successful sign-in
stored nothing and the app sat unchanged. Authorization now drives the UI:
`auto` chains straight into the callback behind a waiting state with a
cancel, and the paste field appears only when a provider actually asks
for a code.

Two smaller failures shared that surface. Prompts were never collected,
which put GitHub Copilot Enterprise out of reach entirely, so a method
that declares them now asks first and passes the answers to authorize.
Device codes are also recovered from the instructions text, where they
actually live — the old code read fields the API does not return, so the
copy button never appeared.

The callback is exempt from the ordinary proxy deadline and gets a
15-minute budget, bounded by the shortest upstream expiry we know of.
A human sign-in with 2FA does not fit in four minutes, and expiring it
turned a completed login into a 504.

packages/ui/src/lib/i18n/messages/de.settings.ts

@@ -1321,6 +1321,17 @@ export const settingsDict = {
   'settings.providers.page.auth.apiKeyPlaceholder': 'sk-...',
   'settings.providers.page.auth.oauthMethodFallback': 'OAuth-Methode {index}',
   'settings.providers.page.auth.pasteAuthorizationCodePlaceholder': 'Autorisierungscode einfügen',
+  'settings.providers.page.auth.oauth.starting': 'Autorisierung wird gestartet …',
+  'settings.providers.page.auth.oauth.waiting': 'Warten auf Autorisierung …',
+  'settings.providers.page.auth.oauth.waitingHint': 'Schließen Sie die Anmeldung im Browser ab. Lassen Sie diese Seite geöffnet – die Verbindung wird von selbst hergestellt.',
+  'settings.providers.page.auth.oauth.codeHint': 'Kopieren Sie den Autorisierungscode aus dem Browser und fügen Sie ihn hier ein.',
+  'settings.providers.page.auth.oauth.deviceCodeLabel': 'Gerätecode',
+  'settings.providers.page.auth.oauth.linkLabel': 'Autorisierungslink',
+  'settings.providers.page.auth.oauth.promptRequired': 'Füllen Sie „{field}“ aus, um fortzufahren',
+  'settings.providers.page.auth.oauth.error.sessionExpired': 'Die Autorisierungsanfrage ist abgelaufen. Verbinden Sie erneut, um sie neu zu starten.',
+  'settings.providers.page.auth.oauth.error.codeRequired': 'Dieser Anbieter benötigt den Autorisierungscode aus Ihrem Browser.',
+  'settings.providers.page.auth.oauth.error.declined': 'Die Autorisierung wurde abgelehnt oder nicht abgeschlossen.',
+  'settings.providers.page.auth.oauth.error.invalidInput': 'Die eingegebenen Angaben wurden abgelehnt.',
   'settings.providers.page.auth.connected': 'Verbunden',
   'settings.providers.page.auth.incomplete': 'Anmeldedaten fehlen',
   'settings.providers.page.auth.incompleteHint': '· Fügen Sie einen API-Schlüssel oder {env:VAR} hinzu, bevor Sie diesen Anbieter im Chat verwenden',
@@ -1351,6 +1362,9 @@ export const settingsDict = {
   'settings.providers.page.actions.open': 'Öffnen',
   'settings.providers.page.actions.copy': 'Kopieren',
   'settings.providers.page.actions.complete': 'Vervollständigen',
+  'settings.providers.page.actions.continue': 'Weiter',
+  'settings.providers.page.actions.cancel': 'Abbrechen',
+  'settings.providers.page.actions.tryAgain': 'Wiederholen',
   'settings.providers.page.actions.hide': 'Ausblenden',
   'settings.providers.page.actions.reconnect': 'Erneut verbinden',
   'settings.providers.page.actions.edit': 'Bearbeiten',
@@ -1365,7 +1379,6 @@ export const settingsDict = {
   'settings.providers.page.toast.apiKeySaved': 'API-Schlüssel gespeichert',
   'settings.providers.page.toast.oauthStartFailed': 'Fehler beim Starten des OAuth-Flows',
   'settings.providers.page.toast.oauthDetailsMissing': 'Keine OAuth-Details zurückgegeben',
-  'settings.providers.page.toast.completeOAuthInBrowser': 'Schließen Sie den OAuth-Flow in Ihrem Browser ab',
   'settings.providers.page.toast.oauthCompleteFailed': 'Fehler beim Abschließen des OAuth-Flows',
   'settings.providers.page.toast.oauthCompleted': 'OAuth-Verbindung abgeschlossen',
   'settings.providers.page.toast.oauthLinkCopied': 'OAuth-Link kopiert',