M1/F1: Kimi Code OAuth device-code flow

Replace the xAI OAuth stack with the Kimi device authorization grant:
- kimi_oauth.rs wire layer (device_authorization + token poll + refresh
  against kigi_env::oauth_host(); client_id per PRD; retryable statuses
  429/5xx with backoff; expired_token restarts authorization)
- X-Msh-Device-{Name,Model,Id} headers; device_id minted uuid4-hex at
  ~/.kigi/device_id (0600)
- Storage: system keyring service `kigi`, entry `oauth/kimi-code`
  (macOS/Windows native backends), atomic-file fallback under ~/.kigi;
  official client's keyring/~/.kimi never touched
- Refresh manager: 60s tick, threshold max(300, expires_in*0.5),
  401-tombstone keyed by rejected refresh token with 300s cooldown and
  rotation auto-clear, cross-process lock with sibling-adoption
  triple-check, sleep/wake forced refresh
- Deleted xAI machinery: enterprise OIDC (PKCE/JWKS/teams), devbox login,
  external auth provider, JWT tier gating + subscription paywall stack,
  X-XAI-Token-Auth marker headers, ZDR gates, /user enrichment
- kigi login / TUI /login both drive the device flow; login-host display
  now derives from kigi_env::oauth_host()
- 264 auth unit/wiremock tests; live contract probe of
  auth.kimi.com/api/oauth/device_authorization matches the wire shapes

Gates: check/clippy --all-targets clean, fmt, deny ok, kigi-shell lib
5131 tests green.

crates/codegen/kigi-tui/src/app/session_startup.rs

@@ -418,9 +418,9 @@ pub(crate) fn pre_acp_auth_manager(
 ) -> std::sync::Arc<kigi_shell::auth::AuthManager> {
     let auth = std::sync::Arc::new(kigi_shell::auth::AuthManager::new(
         &kigi_shell::util::kigi_home::kigi_home(),
-        agent_config.grok_com_config.clone(),
+        agent_config.kimi_code_config.clone(),
     ));
-    auth.configure_refresher(agent_config.grok_com_config.auth_provider_command.clone());
+    auth.configure_refresher();
     auth
 }
 /// Preflight: preferred id must be a UUID and not a persisted session under `cwd`.
@@ -621,7 +621,7 @@ async fn resolve_existing_session(
     use kigi_shell::util::kigi_home::kigi_home;
     let deployment_key = agent_config.endpoints.deployment_key.clone();
     ensure_authenticated_or_noninteractive(
-        &agent_config.grok_com_config,
+        &agent_config.kimi_code_config,
         deployment_key.is_some(),
         None,
     )
@@ -629,7 +629,7 @@ async fn resolve_existing_session(
     .map_err(|e| anyhow::anyhow!("Failed to authenticate for session restore: {}", e))?;
     let auth_manager = std::sync::Arc::new(AuthManager::new(
         &kigi_home(),
-        agent_config.grok_com_config.clone(),
+        agent_config.kimi_code_config.clone(),
     ));
     let registry_client =
         SessionRegistryClient::new(agent_config.endpoints.proxy_url(), String::new())