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/sessions_cmd.rs

@@ -40,11 +40,11 @@ pub async fn run(args: SessionsArgs, agent_config: &AgentConfig) -> Result<()> {
     // for these setups), any cached credential will be used. Otherwise we still
     // proceed so the SessionRegistryClient can use the deployment_key when
     // talking to the custom proxy.
-    let auth = try_ensure_fresh_auth(&agent_config.grok_com_config).await;
+    let auth = try_ensure_fresh_auth(&agent_config.kimi_code_config).await;
 
     let auth_manager = std::sync::Arc::new(AuthManager::new(
         &kigi_home(),
-        agent_config.grok_com_config.clone(),
+        agent_config.kimi_code_config.clone(),
     ));
 
     let client = kigi_shell::agent::session_registry_client::SessionRegistryClient::new(
@@ -169,7 +169,7 @@ pub async fn run(args: SessionsArgs, agent_config: &AgentConfig) -> Result<()> {
             // backend delete is idempotent (a `404` is treated as success),
             // so this is safe for local-only sessions with no remote copy.
             // ZDR teams never upload, so there is nothing remote to delete.
-            let needs_remote = auth.as_ref().is_some_and(|a| !a.is_zdr_team());
+            let needs_remote = auth.is_some();
 
             // Pass `cwd = None` so the session is found by id regardless of
             // which workspace it was created in; the local delete still uses