fix(auth): add accountLinking trustedProviders for authentik (GRO-1509)

Betters Auth v1.5.6 link-account.mjs:22 rejects OAuth callbacks when the
genericOAuth provider is not in trustedProviders AND email_verified is
falsy. Adding authentik to trustedProviders bypasses this guard so OIDC
login works for TF-created users whose emails were never verified through
an authentik flow.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/lib/auth.ts

@@ -251,6 +251,10 @@ export async function initAuth(): Promise<void> {
         },
       },
       account: {
+        accountLinking: {
+          enabled: true,
+          trustedProviders: ["authentik"],
+        },
         storeStateStrategy: "cookie" as const,
       },
       emailAndPassword: {