Rebrand auth guidance strings: grok login/logout -> kigi login/logout

The headless not-signed-in message still pointed at `grok login` and
XAI_API_KEY; error copy across the shell (re-auth prompts, managed-config
rejection, mcp doctor, trace classifier) and kigi-bin did too. All now
reference `kigi login` / `kigi logout`, and the headless fallback points
at the Moonshot open-platform key (KIGI_MOONSHOT_API_KEY).

crates/codegen/kigi-shell/src/config/watcher.rs

@@ -112,7 +112,7 @@ pub enum ConfigChangeEvent {
 /// comparison) skips the update when nothing actually changed, so the
 /// redundant read is harmless. This avoids a class of bugs where an
 /// optimistic suppression window accidentally swallows writes from external
-/// processes (e.g. `grok login` in another terminal).
+/// processes (e.g. `kigi login` in another terminal).
 ///
 /// Adds two **non-recursive** watches per `cwd` argument:
 /// `<cwd>/` (catches `.mcp.json` and `.claude.json` at the project root) and