[FEATURE] Show session color in Session Picker

### Preflight Checklist

- [x] I have searched [existing requests](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20label%3Aenhancement) and this feature hasn't been requested yet
- [x] This is a single feature request (not multiple features)

### Problem Statement

I use the `/color` command to indicate session liveness and type, which makes finding abandoned work in the Agent View very convenient. However, agent view can only see background-launched sessions, and can't list-all. The Session Picker is more complete, but doesn't display colors.

### Proposed Solution

Color is an available piece of session metadata, so it would hopefully be straightforward to show it in the Session Picker list (just as it shows in the Agent View list).

### Alternative Solutions

Being able to search the session picker by color (and possibly other session metadata fields) would also work, and would be a great addition.

### Priority

Medium - Would be very helpful

### Feature Category

Interactive mode (TUI)

### Use Case Example

The title sounds cosmetic but color is a key part of my workflow.

At any given time, I am actively managing 3+ Claude sessions, but have several more paused, waiting on review or stakeholder discussions. I use titles to indicate the primary topic of each session, but I use color to indicate liveness (set non-default at start, return to default when all work is done) and type (e.g. green for coding, purple for tracking/coordination, red for analysis of other devs' PRs . . .)

When I restart my machine, I need to restore work context, and for all sessions visible to Agent View, I can quickly do this at-a-glance - just light up everything that has a color highlight, and ask the agent for current status. But not all sessions appear there, and an important incomplete session could be a week old or more, below dozens of completed sessions in the picker.

With this feature, I could easily use the Session Picker to never lose a work thread.

### Additional Context

I confirmed my understanding of the two session views and feature size with Claude:

1. **Colors aren't shown in session picker** — rows display name/title, summary or first prompt, time since activity, git branch, and file size. No color field, and no toggle to add one. Straight UI limitation.
2. **No way to widen agent view to all sessions** — it's defined as exclusively for background sessions (--bg//bg). There's no documented flag to include foreground/interactive ones.
3. **No way to search by color** — the session picker only searches by name/title, not by color or content
4. __ If it's genuinely new, file it with that same framing: color already exists as session metadata (/color), it's just not surfaced in the one list view that's searchable — a small, concrete ask rather than a big new feature.

Start by locating the Session Picker implementation and the existing color display in the Agent View, then trace how session color metadata is read. Done means the Session Picker visibly shows each session's color while retaining its existing name, summary, activity, branch, and file-size information; check any nearby picker tests if present.

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