§9 acceptance: grep-zero sweep — every internal x.ai/grok identifier renamed

The PRD's first acceptance gate now holds: grep -RinE '\bx\.ai\b|grok'
crates/ --include='*.rs' → 0 matches (exempt: NOTICE and third-party
license archives, README provenance, and the required 'Based on Grok
Build Open Source' attribution, now sourced from version_attribution.txt).

Wire-visible renames (both sides in this repo, changed in lockstep):
- Auth method id 'grok.com' → 'kimi-code' (AuthMethodKind::KimiCode).
- Every x.ai/* and _x.ai/* ACP ext method and meta key → kigi/* /
  _kigi/* (~200 names; grokShell → kigiShell). Session-file replay keeps
  a read-side alias for the legacy '_x.ai/session/update' method so
  existing updates.jsonl histories load; writes emit only the new name
  (both directions test-pinned).
- Agent types grok-build* → kigi* with a documented legacy-prefix alias
  at resolution time so persisted sessions keep resolving.
- ToolNamespace/BuiltinAgentName GrokBuild* → Kigi* (wire snake_case
  kigi/kigi_concise/kigi_hashline; schema regenerated); grok_build
  implementation dirs renamed to kigi*.
- x-grok-* headers → x-kigi-*, __GROK_* sentinels → __KIGI_*, themes
  grokday/groknight → kigiday/kiginight (old persisted values fall back
  to the default theme), web_fetch allowlist xAI hosts → kimi.com +
  moonshot platforms, changelog CDN → this repo, grok-build changelog
  archives deleted.
- BYOK default endpoint removed: [endpoints] api_base_url is now truly
  optional with NO default — consumers fail fast with the flag name when
  unset (no silent x.ai egress). Mock harnesses inject it explicitly.
- System-prompt identity fixed: 'released by xAI' → 'an unofficial
  community CLI for Kimi' (template + regenerated encrypted form).

Also repaired pre-existing grok-era test debt found by the sweep: the
stale trace_classify default-model pin, the grok-pager UA label test,
pty-harness stale-binary reuse and non-hermetic moonshot routing (a PTY
test could previously reach the real api.moonshot.cn), and the outdated
oauth fixture scope key.

Gates: §9 grep 0; fmt clean; workspace check/clippy 0/0 (-D warnings);
FULL cargo test --workspace: 234 suites, 21,961 passed, 0 failed;
deny advisories ok.

crates/codegen/kigi-shell/tests/test_fork_session.rs

@@ -18,7 +18,7 @@ async fn create_test_session(storage: &JsonlStorageAdapter, session_id: &str, cw
         cwd: cwd.to_string(),
     };
 
-    let model_id = acp::ModelId::new("grok-code-fast-1");
+    let model_id = acp::ModelId::new("kigi-code-fast-1");
     storage.init_session(&info, model_id).await.unwrap();
 
     // Add some chat messages
@@ -58,7 +58,7 @@ async fn test_fork_session_creates_new_session_with_parent_tracking() {
 
     let options = kigi_shell::session::storage::CopySessionOptions {
         parent_session_id: Some("source-session-123".to_string()),
-        new_model_id: Some("grok-3".to_string()),
+        new_model_id: Some("kigi-3".to_string()),
         target_prompt_index: None,
         ..Default::default()
     };
@@ -77,7 +77,7 @@ async fn test_fork_session_creates_new_session_with_parent_tracking() {
 
     assert_eq!(loaded.summary.info.id.to_string(), "fork-session-456");
     assert_eq!(loaded.summary.info.cwd, "/new/path");
-    assert_eq!(loaded.summary.current_model_id, acp::ModelId::new("grok-3"));
+    assert_eq!(loaded.summary.current_model_id, acp::ModelId::new("kigi-3"));
     assert_eq!(
         loaded.summary.parent_session_id,
         Some("source-session-123".to_string())