[FEATURE] Desktop Code sidebar: show project folder next to session title when Group by: None

### 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

With Group by: None, sessions are listed by recency, which is the most useful
order — but there's no indication which project each session belongs to.
With 30+ projects, similar titles ("Status and roadmap", "General coding
session") become indistinguishable.

Proposed
- Show a short, muted project folder label next to (or under) each session title
- When space is tight, truncate the session title, not the label
- Clicking the label filters the list to that project

Why
A flat recency list with project labels answers "what was I just working on"
directly, without expanding groups or maintaining group order. Same pattern as
recent files in VS Code / JetBrains (filename + dimmed path).

Environment: Claude Desktop, macOS, Code tab

### Proposed Solution

Show the project folder name next to each session title when Group by is set to None.

Either always, or behind a sidebar option "Show folder name" (in the same popover as Group by / Sort by).

Label rules:
- By default, show only the last segment of the session's working directory
(e.g. `laconic` for `~/src/laconic`).
- If two or more listed sessions have working directories with the same last
segment but different paths, show the shortest path suffix that makes them
distinct (e.g. `work/laconic` vs `personal/laconic`), falling back to the
full path only if needed.
- The full path is always available in a tooltip on hover.
- The label is short and visually muted, so it doesn't compete with the title.
- When horizontal space is tight, truncate the session title first, not the label;
if the label itself must be shortened, truncate from the start, not the end,
so the distinguishing part stays visible.

Related: #83937 — turning grouping off restores a compact list, but then there is
no way to tell which project a session belongs to. This label addresses that.

### Alternative Solutions

_No response_

### Priority

Medium - Would be very helpful

### Feature Category

Other

### Use Case Example

_No response_

### Additional Context

_No response_

The issue names no repository files or tests; start by locating the Claude Desktop macOS Code-tab sidebar and the session-list entry point for Group by: None. Verify how working directories, duplicate folder names, filtering, tooltips, and truncation are represented. Done means distinct project labels appear beside sessions, preserve the specified truncation behavior, and make the label filter the list.

Written by the indexing model from the issue text.