Story 4.7: Display Navigation Breadcrumbs

[ajelinek]

Part of #10

As a user, I want to see breadcrumb navigation that shows my current position within the presentation's hierarchy, especially for nested slides.

Acceptance Criteria:

• A breadcrumb trail is displayed, indicating the path from the presentation root to the current slide.
• Each part of the breadcrumb (representing a parent slide) is clickable to navigate directly to that slide.
• Breadcrumbs update dynamically as the user navigates through the presentation.
• For top-level slides, breadcrumbs might show only the presentation title or be minimal.

Test Cases:

• E2E test: Breadcrumbs correctly show the path for a deeply nested slide.
• E2E test: Clicking a breadcrumb link navigates to the correct parent slide.
• E2E test: Breadcrumbs update when navigating using next/prev, up/down controls.

Constraints:

• Relies on the navigation tree having clear parent-child relationships and slide titles/IDs.

Dependencies:

• Story 3.3 (Build Hierarchical Navigation Tree).
• Story 4.6 (Hierarchical Navigation).