Update VBA Regional office designs to have events and side nav

[davidmpickett]

User Story or Problem Statement

VBA pages don't currently have side navigation menus, because they are essentially single pages. As we add Events, we will need to give these pages side nav menus.

Consider the existing VAMC designs and whether there are any opportunities to update them

Events listing page: https://www.va.gov/chicago-health-care/events/
Specific events page: https://www.va.gov/outreach-and-events/events/62368/
Address any accessibility concerns found in #16346

Description or Additional Context

Steps for Implementation

Acceptance Criteria

• Designs are documented in Figma
• Testable_Outcome_Y
• Testable_Outcome_Z
• Requires design review
• Requires CAIA IA review (likely directly with Mikki, sync with Amanda on this)
• Requires accessibility review