[FEATURE] Code tab sidebar: group sessions by project inside a section

Environment: Claude desktop app, Code tab, macOS

Problem
Sidebar sections are flat. A section can arrange its sessions by date, by state or not at all, but not by project folder. Grouping by project is only offered for the whole sidebar.

I work across several companies, each with many repos. To get two levels today I name sections "Eleshop · crm", "Eleshop · elecommerce" and so on. That makes 14 sections for one company alone, and the sidebar becomes a long list of headers.

Proposal
Let a section group its own sessions by project folder, so the sidebar reads Section > Project > Sessions. Each project inside a section should collapse on its own.

Prior art
The Codex app groups threads under projects in its sidebar.

Related
#39990 asked for project-level organization in the Code tab. It was closed as inactive and is now locked.