§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test could previously reach the real api.moonshot.cn), and the outdated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/api.rs

@@ -968,7 +968,7 @@ fn try_btrfs_remove(
             // Known residual TOCTOU: validation `lstat`s/canonicalizes then we
             // delete by path (the `btrfs subvolume delete` CLI takes a path, not
             // an fd, so there is no `unlinkat` to close the window). Bounded by:
-            // `btrfs` refuses non-subvolumes, the snapshot dir is grok-owned, and
+            // `btrfs` refuses non-subvolumes, the snapshot dir is kigi-owned, and
             // `..`/symlink targets are already rejected. Accepted as-is.
             if let Some(report) = delete_snapshot_with_delegate_fallback(
                 &resolved,
@@ -2186,7 +2186,7 @@ mod tests {
         use kigi_test_utils::git::{git_commit_all, init_git_repo};
         // Isolate KIGI_SHARE_DIR so the post-removal unregister writes to a private DB.
         #[cfg(feature = "metadata")]
-        let _fx = crate::db::GrokHomeFixture::new();
+        let _fx = crate::db::KigiHomeFixture::new();
 
         let tmp = tempfile::TempDir::new().unwrap();
         let repo = tmp.path().join("repo");
@@ -2837,7 +2837,7 @@ mod tests {
         fn register_worktree_writes_correct_fields() {
             // Isolate KIGI_SHARE_DIR so register_worktree's open_default write lands
             // in our own DB (lock + private tmp + restore via the fixture).
-            let fx = crate::db::GrokHomeFixture::new();
+            let fx = crate::db::KigiHomeFixture::new();
 
             // Unique basename → unique id, so a concurrent open_default writer
             // (KIGI_SHARE_DIR is process-global) can't INSERT-OR-REPLACE our row.
@@ -3411,7 +3411,7 @@ mod tests {
             // remove_worktree must keep the DB record when the on-disk removal
             // fails, so the worktree isn't lost from tracking while leaking on
             // disk (unregister only after a successful removal).
-            let fx = crate::db::GrokHomeFixture::new();
+            let fx = crate::db::KigiHomeFixture::new();
 
             // A regular file makes remove_dir_all fail (ENOTDIR) deterministically.
             let wt_path = fx.home.join("doomed-wt");
@@ -3454,7 +3454,7 @@ mod tests {
             kigi_test_utils::require_git!();
             use kigi_test_utils::git::{git_commit_all, init_git_repo};
 
-            let fx = crate::db::GrokHomeFixture::new();
+            let fx = crate::db::KigiHomeFixture::new();
 
             // A real repo + a real worktree so remove_worktree succeeds on disk.
             let repo = fx.home.join("repo");
@@ -3504,7 +3504,7 @@ mod tests {
 
             // KIGI_SHARE_DIR == the gc DB dir so remove_worktree's open_default
             // unregister hits the same DB the gc record lives in.
-            let fx = crate::db::GrokHomeFixture::new();
+            let fx = crate::db::KigiHomeFixture::new();
             let db = WorktreeDb::open(&fx.home).unwrap();
 
             let dir = fx.home.join("expired-wt");