Route third-party first-run setup into the provider wizard (#261)

The login picker previously sent third-party users to a dead-end info screen
that only mentioned env vars. This change reuses the existing provider wizard
from the login flow so first-run setup can continue without requiring slash
command access first.

Constraint: The existing provider setup logic must remain the single source of truth
Rejected: Build a separate third-party auth wizard in ConsoleOAuthFlow | would duplicate provider setup behavior and drift over time
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep third-party onboarding routed through ProviderWizard unless the provider command flow is intentionally redesigned
Tested: bun test src/components/ConsoleOAuthFlow.test.tsx src/commands/provider/provider.test.tsx
Tested: tsc --noEmit via project diagnostics
Not-tested: Live gh-authenticated push and PR creation path

Co-authored-by: anandh8x <test@example.com>

src/commands/provider/provider.tsx

@@ -903,7 +903,11 @@ function resolveCodexCredentials(processEnv: NodeJS.ProcessEnv):
   }
 }
 
-function ProviderWizard({ onDone }: { onDone: LocalJSXCommandOnDone }): React.ReactNode {
+export function ProviderWizard({
+  onDone,
+}: {
+  onDone: LocalJSXCommandOnDone
+}): React.ReactNode {
   const defaults = getProviderWizardDefaults()
   const [step, setStep] = React.useState<Step>({ name: 'choose' })