Event navbar for 2026 Winter Olympics

[frederickobrien]

With the Winter Olympics fast approaching this follows up on #15200 by wiring up an event navigation bar on the appropriate fronts and pages.

A few things to consider:

• How best to identify the pages we want this to appear on. IDs? Packages? Something solid that doesn't change if article paths are updated
• @adi-gnm raised a couple of great points about app functionality. Do the links work as expected, and is the component accessible? 'Touch targets in the app are expected to be at least 48x48px (Android) and 44x44px (iOS)'

This is something of a test case so there's room to iterate and evolve, but we need something operational before the event starts.