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test could previously reach the real api.moonshot.cn), and the outdated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

@@ -141,7 +141,7 @@ pub fn create_snapshot_with_symlink(btrfs_info: &BtrfsInfo, dest: &Path) -> Resu
             })?;
         } else if !is_safe_snapshot_delete_target(&snapshot_path) {
             bail!(
-                "refusing to delete pre-existing snapshot {}: outside grok-managed \
+                "refusing to delete pre-existing snapshot {}: outside kigi-managed \
                  btrfs storage",
                 snapshot_path.display()
             );
@@ -251,7 +251,7 @@ pub fn snapshot_dest_path(btrfs_mount: &Path, subvolume_root: &Path, dest: &Path
 ///
 /// Symlinks cross mount namespaces and persist across process exits, so the
 /// worktree at `dest` stays visible to the user's other shells and survives a
-/// grok restart.
+/// kigi restart.
 ///
 /// Destructive contract: a pre-existing **stale symlink** at `dest` is unlinked;
 /// a pre-existing **directory** is removed only if empty (`remove_dir`). A
@@ -351,7 +351,7 @@ pub fn delete_snapshot(path: &Path) -> Result<()> {
 ///   canonicalized parent's final component is one of [`BTRFS_SNAPSHOT_SUBDIRS`]
 ///   (`worktrees` or `.kigi-snapshots`),
 /// - and that directory sits **directly under a real btrfs mount point** (from
-///   the live mount table), anchoring the delete to grok-managed storage rather
+///   the live mount table), anchoring the delete to kigi-managed storage rather
 ///   than any directory that merely happens to be named `worktrees`.
 ///
 /// Treat all symlink targets and metadata paths as untrusted input and pass