Reject edits that win by darkening the rest of the ad

[EnesYilmazcode]

The README's Nike 59 to 81 edit won by dimming everything outside the logo (brightness 0.17x, color 0.07x of the original), and the guard let it through.

• eval_guard.py now compares brightness, contrast, color and detail outside the brand box, cell by cell on an 8x8 grid, so dimming the scene fails but removing one object passes. Both callers pass the target box.
• Tests cover darken, desaturate, blur, black-out, an inside-only edit, and real recorded edits including the June Nike one.
• Re-judged the recorded runs: Apple's background swap is no longer kept.
• New honest win in the README: a Red Bull edit that clears the desk, 79 to 82. Every-edit strip now uses a Red Bull run. The Ordinary sample is removed.
• Demo now serves from its own site, https://pixel-gaze.web.app/