Charity Auction Promotion Easter Egg or Mode

## Summary
BigAdam has requested a charity promotion Easter Egg advertising the auction. His request is:

"I have a dream of a goofy swadge easter egg for the charity team.  SOMETHING to lead to a still image or even just text if it's easier, promoting the auction.  I even had the idea of using the swadgepass interface as the trigger, if possible.  If someone made their name HUEYHUEYHUEY it would pop the easter egg."

## Technical Spec
Adam is suggesting using some sort of beacon or swadgepass functionality to trigger it, perhaps it can be at the charity booth?
This could play a sound I suppose, and the zanier the better.

I think this is a very open-ended prompt that could be shoved into several things. Hell, it could have its own mini game if we wanted. Tap A to throw money at Adam in a PG way?

## UI
I am envisioning this having its own mode with an image or animation. Perhaps a Huey swadgepass would trigger it?

Otherwise, it could be something like a solution to a puzzle, a hidden room in a game, or something else.

## Mockups
none yet, should request pixel art of the charity gang and an ad.

## How to Test

No files or tests are named in the issue. Start by reading the repo docs/README and locating where game modes and input/event handling are defined, especially any passcode, beacon, or easter-egg-style triggers. Find a suitable hidden-mode registration path, then implement a minimal charity-auction promo mode behind the HUEYHUEYHUEY trigger. Done when entering that trigger cleanly opens the promo behavior (text/image/sound) and the normal firmware build/test flow passes.

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