§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test could previously reach the real api.moonshot.cn), and the outdated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/docs/user-guide/README.md

@@ -1,6 +1,6 @@
-# Grok Build User Guide
+# Kigi User Guide
 
-Learn how to install, configure, and extend Grok Build, the terminal-based AI coding assistant from SpaceXAI.
+Learn how to install, configure, and extend Kigi, the terminal-based AI coding assistant from SpaceXAI.
 
 ---
 
@@ -20,7 +20,7 @@ Start here. These guides cover what you need on your first day.
 
 ## Tier 2: Core Feature Docs
 
-Customize and extend Grok Build.
+Customize and extend Kigi.
 
 | # | Document | Description |
 |---|----------|-------------|
@@ -37,11 +37,11 @@ Customize and extend Grok Build.
 
 ## Tier 3: Advanced Usage Docs
 
-Automate, script, and integrate Grok Build with other systems.
+Automate, script, and integrate Kigi with other systems.
 
 | # | Document | Description |
 |---|----------|-------------|
-| 14 | [Headless Mode and Scripting](14-headless-mode.md) | `grok -p`, output formats, CI/CD integration, and piping |
+| 14 | [Headless Mode and Scripting](14-headless-mode.md) | `kigi -p`, output formats, CI/CD integration, and piping |
 | 15 | [Agent Mode and IDE Integration](15-agent-mode.md) | ACP stdio transport, WebSocket relay, and SDK integration |
 | 16 | [Subagents and Personas](16-subagents.md) | Parallel child sessions, agent types, personas, and capability modes |
 | 17 | [Session Management](17-sessions.md) | Save, load, resume, rewind, compact, and the session persistence format |