[onevcat]

Summary

Sidebar groups were only creatable from a project's menu, and a group's members looked the same as top-level projects. This adds two direct ways to create a group and makes the hierarchy clearer.

• Sidebar context menu. Right-click the empty part of the list: New Group, Add Repository, Clone Repository, Add Remote Project, Add Workspace, Expand All, Collapse All, Show or Hide Active Agents, Refresh Worktrees, Archived Worktrees. Add actions go straight to their own UI, not the add panel. Rows with their own menu keep it.
• Add panel. New "Add Project Group" option. It asks for a name, then adds an empty group.
• Empty groups go to the end of the list and scroll into view. Canceling the name prompt adds nothing. The placeholder now says "Drag projects here to add them".
• Indent. Group members move in 10 pt, and their worktrees move with them. The drop target still covers the indent.
• Folder icon. Filled when collapsed, outline when open.
• Group Color menu. Each option has a color dot; None has an empty circle.

The group name stays in the proportional font: every other name in the sidebar uses it, and a group name is a free-form label, not an identifier.

New copy is English until the release sync-l10n run adds translations.

Screenshots

Context menu	Add panel

Empty and collapsed groups	Member indent	Color menu

Verification

• make check, make test, and make build-app pass. New reducer and layout tests cover the empty group flow, including with no repositories.
• In an isolated Debug instance: right-click on the empty area and on a project header, create a group from the menu and from the panel, drag a project onto the placeholder, open the clone sheet, and check the color dots.
• Not checked in the app: the scroll into view (reducer test only), and the panel option from the no-repositories empty state.