Group recent sessions in sidebar by project / working directory

Problem
When working on multiple projects at the same time, the Recent Sessions list in the left sidebar mixes sessions from all working directories together, sorted only by recency. It's easy to resume the wrong session and start editing in the wrong repo, or to lose track of which in-flight session belongs to which project.

Requested behavior
Add a way to organize recent sessions in the sidebar by project (cwd / git repo root):

• Group sessions under collapsible project headers (path or repo name), with sessions inside each group sorted by recency.
• Or a toggle/setting to switch between "Sort by recency" (current) and "Group by project".
• Optional: filter to show only the current project's sessions, or pin a project to the top.
• Show the project name/path on each session row regardless of grouping mode, so the active project is always unambiguous.

Why it matters

• Prevents cross-project mistakes (editing/committing in the wrong repo).
• Makes parallel work across repos viable without constantly re-reading paths.
• Matches how IDEs (VS Code, JetBrains) already organize recent workspaces.

Environment

• Claude Code CLI on macOS (Darwin 25.4.0)