fix(tui): raise neutral permission backgrounds

[jlongster]

Summary

• add a mode-aware themeV2.raise(color) utility alongside increase and decrease
• replace duplicated light/dark color-step logic across session and prompt surfaces
• raise permission action footers from their contextual neutral background instead of using the focused interactive color

Verification

• bun typecheck in packages/tui
• bun test test/theme/v2/component.test.ts in packages/tui
• reproduced the permission prompt with opencode-drive; the footer is neutral and only the selected action retains the interactive highlight

[jlongster]

Verified on the PR branch with OpenCode Drive. The permission footer now uses the raised neutral background, while the selected action retains the interactive highlight.