§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test could previously reach the real api.moonshot.cn), and the outdated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-fast-worktree/src/worktree/execute.rs

@@ -220,7 +220,7 @@ pub(crate) fn execute_create_worktree(plan: WorktreePlan) -> Result<CreateWorktr
     Ok(result)
 }
 
-/// Record the source repo root in `<worktree>/.git/grok-worktree-source`.
+/// Record the source repo root in `<worktree>/.git/kigi-worktree-source`.
 ///
 /// A standalone worktree is an independent repo whose `.git` is a directory:
 /// nothing inside it points back to the source, so consumers like `.envrc`
@@ -234,7 +234,7 @@ fn record_main_repo_marker(source: &Path, worktree: &Path) {
     if !git_dir.is_dir() {
         return;
     }
-    let marker = git_dir.join("grok-worktree-source");
+    let marker = git_dir.join("kigi-worktree-source");
     if marker.exists() {
         return;
     }
@@ -1685,7 +1685,7 @@ mod tests {
 
         record_main_repo_marker(&source, &dest);
 
-        let marker = dest.join(".git/grok-worktree-source");
+        let marker = dest.join(".git/kigi-worktree-source");
         let recorded = std::fs::read_to_string(&marker).expect("marker should be written");
         assert!(
             Path::new(recorded.trim()).join(".git").is_dir(),
@@ -1704,7 +1704,7 @@ mod tests {
 
         record_main_repo_marker(&source, &dest);
 
-        assert!(!dest.join(".git/grok-worktree-source").exists());
+        assert!(!dest.join(".git/kigi-worktree-source").exists());
     }
 
     #[test]
@@ -1717,7 +1717,7 @@ mod tests {
 
         let dest = tmp.path().join("dest");
         std::fs::create_dir_all(dest.join(".git")).unwrap();
-        let marker = dest.join(".git/grok-worktree-source");
+        let marker = dest.join(".git/kigi-worktree-source");
         std::fs::write(&marker, "/the/ultimate/main/repo").unwrap();
 
         record_main_repo_marker(&source, &dest);