feat: lower opacity for thinking summaries

[remorses]

Fixes #4542

[Copilot]

Pull request overview

This PR enhances the visual styling of thinking summaries in the TUI by making them more subtle while maintaining color saturation. Instead of blending syntax highlight colors with the background (which washes them out), it now uses transparency (alpha channel set to 100/255, approximately 39% opacity) to achieve a visually subtle appearance.

• Adds a new generateSubtleSyntax function that creates a subtle variant of syntax highlighting by applying transparency
• Updates the ReasoningPart component to use the new subtle syntax style
• Refactors syntax rule generation into a shared getSyntaxRules helper function

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/opencode/src/cli/cmd/tui/context/theme.tsx	Adds generateSubtleSyntax function and getSyntaxRules helper; exports subtleSyntax from theme context
packages/opencode/src/cli/cmd/tui/routes/session/index.tsx	Updates ReasoningPart to use subtleSyntax instead of syntax and theme.textMuted for text color

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.