Add breadcrumbs in the workspace top bar

[priethor]

Goal

Pages can nest several levels deep, and the workspace mixes pages, collections, and row detail surfaces. The only context the canvas gives you today is the current title. Put breadcrumbs in the workspace top bar so you always know where you are and can jump back up.

Scope

• Breadcrumb in the top bar, left side, paired with the document actions on the right.
• Works on every canvas surface: pages, full-page collections, and the row detail surface.
• Pages walk their parent chain; collections sit flat under the workspace root; row detail surfaces show their parent collection plus the row title.
• Each segment is clickable and jumps to that page or collection.
• Long chains truncate in the middle with an ellipsis so the bar doesn't overflow.
• Stays visible regardless of canvas scroll.

Out of scope

• Click-to-rename or drag-to-move from breadcrumb segments.
• Showing the breadcrumb above the page title inside the canvas. The top bar serves the same need across all surfaces.

Acceptance criteria

• On a nested page, the top-bar breadcrumb shows its ancestors back to the workspace root.
• On a full-page collection, the breadcrumb shows the workspace root and the collection.
• On a row detail surface, the breadcrumb ends with the parent collection plus the row title.
• Clicking an ancestor jumps to that page or collection.
• Deep hierarchies don't overflow the top bar.