Rebrand auth guidance strings: grok login/logout -> kigi login/logout

The headless not-signed-in message still pointed at `grok login` and
XAI_API_KEY; error copy across the shell (re-auth prompts, managed-config
rejection, mcp doctor, trace classifier) and kigi-bin did too. All now
reference `kigi login` / `kigi logout`, and the headless fallback points
at the Moonshot open-platform key (KIGI_MOONSHOT_API_KEY).

crates/codegen/kigi-shell/src/util/kigi_auth_credentials.rs

@@ -68,7 +68,7 @@ impl KigiAuthCredentials {
         if self.deployment_key.is_some() {
             "Your KIGI_DEPLOYMENT_KEY is invalid or expired. Please contact a team admin."
         } else if self.user_token.is_some() {
-            "Your auth token is invalid or expired. Run `grok login` to re-authenticate."
+            "Your auth token is invalid or expired. Run `kigi login` to re-authenticate."
         } else {
             "Not authenticated."
         }