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-shell/src/remote/workspaces_client.rs

@@ -77,7 +77,7 @@ impl WorkspacesClient {
 
     pub async fn list_workspaces(&self, q: &WsQuery) -> Result<ListWorkspacesPage, WsError> {
         let auth = self.auth.auth().await.map_err(|_| WsError::NoOauth)?;
-        if !auth.is_xai_auth() {
+        if !auth.is_session_auth() {
             return Err(WsError::NoOauth);
         }
 
@@ -98,10 +98,6 @@ impl WorkspacesClient {
             .get(&url)
             .query(&query)
             .header("Authorization", format!("Bearer {}", auth.key))
-            .header(
-                "X-XAI-Token-Auth",
-                self.auth.grok_com_config().token_header.clone(),
-            )
             .header("x-userid", &auth.user_id)
             .header("x-grok-client-version", kigi_version::VERSION)
             .header(