fix(tui): raise picker selection contrast with inverse + bold

Selected rows in the model/session/skills pickers and approval/clarify
prompts only changed from dim gray to cornsilk, which reads as low
contrast on lighter themes and LCDs (reported during TUI v2 blitz).

Switch the selected row to `inverse bold` with the brand accent color
across modelPicker, sessionPicker, skillsHub, and prompts so the
highlight is terminal-portable and unambiguous. Unselected rows stay
dim. Also extends the sessionPicker middle meta column (which was
always dim) to inherit the row's selection state.

ui-tui/src/lib/platform.ts

@@ -13,7 +13,7 @@ export const isMac = process.platform === 'darwin'
 
 /** True when the platform action-modifier is pressed (Cmd on macOS, Ctrl elsewhere). */
 export const isActionMod = (key: { ctrl: boolean; meta: boolean; super?: boolean }): boolean =>
-  (isMac ? key.meta || key.super === true : key.ctrl)
+  isMac ? key.meta || key.super === true : key.ctrl
 
 /**
  * Some macOS terminals rewrite Cmd navigation/deletion into readline control keys.