Story 4.4: Add Keyboard Navigation Support (Next/Previous, Up/Down)

[ajelinek]

Part of #10

As a user, I want to navigate through slides using keyboard arrow keys (e.g., Right/Left for next/previous, Up/Down for vertical/nested navigation if applicable).

Acceptance Criteria:

• Pressing the Right Arrow key (or Space, PageDown) navigates to the next slide.
• Pressing the Left Arrow key (or PageUp) navigates to the previous slide.
• If hierarchical slides exist:
  • Pressing the Down Arrow key navigates into a child/nested slide.
  • Pressing the Up Arrow key navigates out to a parent slide.
• Keyboard focus is managed appropriately for accessibility.

Test Cases:

• E2E test: Keyboard shortcuts for next/previous slide work.
• E2E test (if hierarchical): Keyboard shortcuts for up/down navigation into/out of nested slides work.
• Accessibility test: Keyboard navigation is intuitive and focus indicators are clear.

Constraints:

• JavaScript event handling required for keyboard input.

Dependencies:

• Story 4.3 (Core Navigation Controls), potentially Story 4.6 (Hierarchical Navigation).