Add 404 easter egg page

[tkodev]

Issue

The site has no custom 404 page. Add a fun, on-brand easter egg experience. Ideas:

• fish aquarium
• interactive game
• fun animations

so that hitting a broken link feels intentional rather than broken.

Design direction

• Theme: fish aquarium or similar playful interactive element
• Should feel like a TechTank moment, not a generic error page
• Must still clearly communicate "page not found" and offer a path back (e.g. link to home)
• Keep it accessible — animation should respect prefers-reduced-motion

Implementation

• Next.js App Router custom 404: app/not-found.tsx
• Any game/animation logic should be self-contained in a component under components/

Acceptance criteria

• app/not-found.tsx created and renders the custom 404 experience
• Page includes a clear "Page not found" message and a link back to /
• Interactive element (aquarium/game) works on desktop and mobile
• Animation/motion respects prefers-reduced-motion: reduce
• Page uses semantic colour tokens (no hardcoded hex)

[Justin-Bento]

A potential Easter egg idea. We could use the mouse as a lightbulb that finds the fish (our logo) hidden underneath the lightbulb. Then just use a section header with some text in the middle of thr page. @tkodev