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/__tests__/platform.test.ts

@@ -5,6 +5,7 @@ const originalPlatform = process.platform
 async function importPlatform(platform: NodeJS.Platform) {
   vi.resetModules()
   Object.defineProperty(process, 'platform', { value: platform })
+
   return import('../lib/platform.js')
 }