[Bug] Sidebar session grouping uses git root instead of session subdirectory

Bug Description
[Bug + Feature Request] Desktop sidebar grouping & hierarchical display

Version: Claude Code 2.1.92
OS: macOS

--- Bug ---
Expected behavior:
Sessions opened in a subdirectory (e.g., /Users/me/repo/consulting/new-clients/)
should appear under that subdirectory name in the sidebar groups,
as they did until 2026-04-21.

Actual behavior (as of 2026-04-22):
Sessions now appear grouped under the parent git repository root name
(e.g., "repo") regardless of the cwd subdirectory.

Note: Data layer seems healthy — ~/.claude/projects/ correctly stores the
session under the cwd-specific directory. Only the sidebar grouping UI
displays them under the git root.

Repro:

1. cd into a subdirectory of a git repo
2. Start a new Claude Code session
3. Observe sidebar — session is grouped under the git root, not the subdirectory

Related: Issue #51539 (worktree sessions in "Other" group) may share a cause.

--- Feature Request ---
Ideally, the sidebar should display folders hierarchically (tree view):
a parent folder expands to show its subfolders as nested children, so users
can navigate the directory structure rather than seeing a flat list of group
names. For example:
repo/
└ consulting/
└ new-clients/
└ (sessions)

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.92
• Feedback ID: 0852a68e-33a2-42a7-a8b3-d5260fdbe588

Errors

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