Better rendering in tmux and ghostty

[dgageot]

This requires a well configured tmux with:

export TERM=xterm-256color
export LANG=en_US.UTF-8
export COLORTERM=truecolor

[docker-agent]

Review Summary

Assessment: 🟡 NEEDS ATTENTION

This PR simplifies terminal rendering by removing multiplexer detection logic (tmux/screen) and associated workarounds. The changes remove FPS throttling and ASCII spinner fallbacks that were previously used for multiplexers.

Findings

1 NOTABLE issue found:

• MEDIUM: Scrollbar thumb and track now use identical characters, potentially making the thumb invisible in certain terminal themes

Analysis

The PR removes:

• inMultiplexer() detection functions from both cmd/root/new.go and pkg/tui/components/spinner/spinner.go
• FPS throttling (30 FPS cap) for multiplexers
• ASCII fallback for spinners (now always uses Braille characters)

The scrollbar change from ┃ to ⎪ for the thumb character creates a visual distinction issue, as both thumb and track now use the same glyph and rely solely on color/style differences.

Recommendation

Review the scrollbar thumb character change to ensure adequate visual distinction across different terminal themes and configurations.

[docker-agent]

Scrollbar thumb and track use identical character

The scrollbar thumb and track now both use the same character (⎪) after changing from thumbChar: "┃" to thumbChar: "⎪".

The thumb and track are now only distinguished by their styles:

• Track: BorderSecondary foreground color
• Thumb: Info foreground color with BackgroundAlt background and bold styling

Issue: If these colors are similar in a particular theme, or if the terminal doesn't render the bold/background styling clearly, the thumb will be difficult or impossible to see against the track since they use the same glyph.

The original ┃ (box drawings heavy vertical, U+2503) was a visually heavier/bolder character that provided clear visual distinction even with similar colors. The new ⎪ (right vertical box line, U+23AA) is the same as the track character, reducing visual distinction to style-only.

Recommendation: Consider using a visually distinct character for the thumb (like the original ┃ or another heavier glyph) to ensure the scrollbar remains usable across different terminal themes and configurations.