Project page rebuild, Library, and real screenshots

I rebuilt the project page: a header band, a Details rail, a stack of peek cards, an activity timeline, and a rich text editor for notes. Scanning moved off the main thread, so the app stays responsive during a scan, and the parser now reads backup metadata and sample paths. The Library became a tabbed page with Workspaces, Collections, Checklists, and Layouts, with a layouts editor that stamps a layout onto a workspace. The landing page uses real product screenshots, Insights gained Consistency and Signature share cards, and a subscription can be cancelled and resumed from the pricing page.