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test could previously reach the real api.moonshot.cn), and the outdated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

@@ -203,7 +203,7 @@ impl WorktreeDb {
 
     /// Open the default DB at `~/.kigi/worktrees.db`.
     ///
-    /// Discovers grok home via `$KIGI_SHARE_DIR`, falling back to the canonicalized
+    /// Discovers kigi home via `$KIGI_SHARE_DIR`, falling back to the canonicalized
     /// `$HOME/.kigi` (matching `kigi_config::kigi_home`).
     /// Path is resolved fresh each call (~1µs env var read) to support
     /// test overrides. Each call opens its own connection — callers in hot
@@ -365,23 +365,23 @@ static KIGI_SHARE_DIR_ENV_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(())
 /// `Drop` restores `KIGI_SHARE_DIR` before `_lock` releases, so the env is correct
 /// before another waiting setter proceeds.
 #[cfg(test)]
-pub(crate) struct GrokHomeFixture {
+pub(crate) struct KigiHomeFixture {
     _lock: std::sync::MutexGuard<'static, ()>,
     prev: Option<std::ffi::OsString>,
-    /// The isolated grok home; pass to `WorktreeDb::open` to read the same DB
+    /// The isolated kigi home; pass to `WorktreeDb::open` to read the same DB
     /// `open_default()` writes to.
     pub home: PathBuf,
     _tmp: tempfile::TempDir,
 }
 
 #[cfg(test)]
-impl GrokHomeFixture {
+impl KigiHomeFixture {
     pub(crate) fn new() -> Self {
         let lock = KIGI_SHARE_DIR_ENV_LOCK
             .lock()
             .unwrap_or_else(|e| e.into_inner());
         let tmp = tempfile::TempDir::new().unwrap();
-        let home = tmp.path().join("grok-home");
+        let home = tmp.path().join("kigi-home");
         std::fs::create_dir_all(&home).unwrap();
         // Warm up the DB (journal-mode conversion + schema) before exposing it
         // via KIGI_SHARE_DIR, sparing the test hot loop set_journal_mode's retry
@@ -401,7 +401,7 @@ impl GrokHomeFixture {
 }
 
 #[cfg(test)]
-impl Drop for GrokHomeFixture {
+impl Drop for KigiHomeFixture {
     fn drop(&mut self) {
         unsafe {
             match self.prev.take() {