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-chat-state/src/types.rs

@@ -102,7 +102,7 @@ impl Default for PruningConfig {
 #[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum AuthType {
-    /// From AuthManager (grok login, OIDC, external binary). Refreshable.
+    /// From AuthManager (kigi login, OIDC, external binary). Refreshable.
     #[default]
     SessionToken,
     /// From user config ([model.*] api_key, env_key, XAI_API_KEY). Not refreshable.