§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test could previously reach the real api.moonshot.cn), and the outdated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-tui/src/views/modal_window.rs

@@ -572,7 +572,7 @@ fn render_tab_bar(
             // not `theme.gray_dim`. At ANSI16 `gray_dim` collapses to the
             // softer slot (silver on White) which leaves text at ~1.2:1
             // contrast — fine for the modal frame's one-cell border line
-            // but unreadable as text glyphs on grokday.
+            // but unreadable as text glyphs on kigiday.
             let style = if is_active {
                 if state.tabs_focused && !is_embedded {
                     Style::default()
@@ -1210,7 +1210,7 @@ mod tests {
         use ratatui::layout::Rect;
 
         let theme = Theme::current();
-        const TEXT: &str = "Tip · Ask Grok about the docs";
+        const TEXT: &str = "Tip · Ask Kigi about the docs";
         let row_text = |width: u16| {
             let area = Rect {
                 x: 0,
@@ -1229,7 +1229,7 @@ mod tests {
         let start = wide.find("Tip").expect("Tip");
         let trailing = wide.chars().rev().take_while(|c| *c == ' ').count();
         assert!(start.abs_diff(trailing) <= 1, "not centered: {wide:?}");
-        assert!(wide.contains("Ask Grok about the docs"));
+        assert!(wide.contains("Ask Kigi about the docs"));
 
         let tiny = row_text(10);
         assert!(tiny.contains("Tip"));