feat(ui): Add thinking/reasoning block visibility toggle

[sauerdaniel]

Summary

Adds keyboard shortcut Ctrl+i to toggle thinking mode visibility in the TUI interface.

Fixes #9140

Problem

Currently, there's no quick way to toggle thinking mode visibility while using the TUI. Users have to navigate through menus to change this setting.

Solution

Add a keyboard shortcut Ctrl+i that toggles thinking mode visibility, similar to how other quick settings work in the TUI.

Changes

• packages/opencode/src/cli/cmd/tui/app.tsx - Add Ctrl+i keybinding to toggle thinking visibility

Testing

• [x] TypeScript compilation passes (bun turbo typecheck)
• [x] Unit tests pass (725 tests, 0 failures)

Note: Manual TUI testing (verifying the keybinding works) was not performed.