§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test could previously reach the real api.moonshot.cn), and the outdated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/src/bin/chat-history-downgrade.rs

@@ -250,13 +250,13 @@ mod tests {
     /// it from the raw JSON to preserve downstream data fidelity.
     #[test]
     fn test_assistant_with_reasoning() {
-        let v1 = r#"{"type":"assistant","content":"The answer is 42.","reasoning":{"text":"Let me think..."},"tool_calls":[],"model_id":"grok-3"}"#;
+        let v1 = r#"{"type":"assistant","content":"The answer is 42.","reasoning":{"text":"Let me think..."},"tool_calls":[],"model_id":"kigi-3"}"#;
         let out = convert_line_for_test(v1);
         let v = v0_value(&out);
         assert_eq!(v["role"], "assistant");
         assert_eq!(v["content"], "The answer is 42.");
         assert_eq!(v["reasoning_content"], "Let me think...");
-        assert_eq!(v["model_id"], "grok-3");
+        assert_eq!(v["model_id"], "kigi-3");
     }
 
     /// Current shape: reasoning is a sibling line
@@ -274,7 +274,7 @@ mod tests {
         );
         assert_eq!(pending.len(), 1);
 
-        let a_line = r#"{"type":"assistant","content":"The answer is 42.","tool_calls":[],"model_id":"grok-3"}"#;
+        let a_line = r#"{"type":"assistant","content":"The answer is 42.","tool_calls":[],"model_id":"kigi-3"}"#;
         let a = convert_line(a_line, &mut pending)
             .unwrap()
             .expect("assistant line produces a v0 message");