Add project-owner breadcrumbs and owner project listings

Goal

Make ownership and navigation clear when a user views a project owned by another profile.

Acceptance criteria

• For a project not owned by the viewer's current profile, breadcrumbs insert the owner's username immediately after Projects.
• The owner crumb links to a page listing that owner's projects that the current viewer is allowed to access.
• Projects owned by the current profile retain the existing breadcrumb shape without a redundant username crumb.
• The owner project listing never reveals inaccessible or deleted projects.
• The crumb and listing work for writable members, read-only members, and public projects under the intended access rules.
• Preserve existing breadcrumb styling, responsive behavior, keyboard focus, and dark-mode states.
• Add authorization and render tests for own project, another owner's accessible projects, mixed accessible/inaccessible projects, and unknown owners.