[FEATURE] Tab groups — organize and color-code tabs by project

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When working on multiple projects at the same time, all tabs look the same. There's no way to group them by project or tell them apart at a glance without reading every tab name.

Proposed Solution

Allow users to create tab groups and assign a color to each group. Tabs in the same group would be visually connected so you can instantly see which tabs belong to which project.

Alternative Solutions

Currently the only option is renaming tabs manually with /rename. There's no visual grouping or color coding.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

1. I have 5 tabs open across 3 projects
2. I create a group for each project and give each one a different color
3. I drag my tabs into their groups
4. I can instantly see which tabs belong to which project without reading every name

Additional Context

_No response_