Rebrand hero banner PNG to TrueMemory

Regenerated assets/charts/hero-banner.png from the source HTML at
/Users/j/Desktop/neuromem/assets/charts/hero-banner-white.html after
swapping the NEUROMEM ANSI-shadow ASCII art for TRUEMEMORY. Background,
grain canvas, typography, transform scale, and layout preserved exactly.

- Source HTML: hero-banner-white.html
- Dimensions: 1200x400 (identical to the pre-rebrand version)
- Rendered via headless Chromium (Playwright) at device_scale_factor=1

Author: buildingjoshbetter