Rebrand remaining user-visible Grok strings to Kigi/Kimi

The welcome hero subtitle still read "Thanks for trying Grok Build";
theme display names, the NO_COLOR/COLORTERM diagnostics notes, the
permission notification title, the self-update restart hints, and the
clipboard-wrap protocol marker all still said Grok. Canonical theme keys
(groknight/grokday) are unchanged — only display strings move.

crates/codegen/kigi-tui/src/views/welcome/hero_box.rs

@@ -23,7 +23,7 @@ const H_INSET: u16 = 2;
 /// Horizontal gap (cols) between the logo and the right column inside the box.
 const LOGO_H_PAD: u16 = 3;
 
-const HERO_SUBTITLE: &str = "Thanks for trying Grok Build, give feedback with /feedback!";
+const HERO_SUBTITLE: &str = "Thanks for trying Kigi, give feedback with /feedback!";
 
 use super::{PROMPT_HEIGHT, VERSION_GAP};