docs: simplify banner to grid + archway logo + wordmark

[johnnyhuy]

Summary

Replaced the previous banner (which had too much text: version tag, subtitle, three stat tags, dashboard mockup) with the minimal version. Just the wordmark, a proper logo, and a subtle grid background.

Before

• v0.1.0 / MIT / OpenAI-compatible tag
• Subtitle (two lines)
• Three orange stat tags (12k req/s, 0ms overhead, 5+ providers)
• Dashboard mockup with 2x2 metric cards

After

• Subtle grid of plus signs (graph paper feel, very low contrast)
• Bold white sans-serif OPENGATEWAY wordmark, centered
• Small white outline archway icon to the left (a gateway shape: two vertical lines with a horizontal bar across the top, like an open door frame)
• One tiny orange dot inside the G (subtle accent, model-added)

The result is a quiet, editorial banner. The grid gives it texture and tech feel without being noisy. The archway icon is the first proper logo OpenGateway has had.

Generation

export FAL_KEY=...
../scripts/generate_banner.py \
  "Wide cinematic banner for OpenGateway AI gateway, 21:9 aspect ratio. Pure black background with a very subtle faint grid pattern of small plus signs across the entire banner (graph paper feel, very low contrast). Centered: a bold white sans-serif wordmark reading OPENGATEWAY. To the left of the wordmark: a small simple white outline icon, a clean geometric mark shaped like a doorway or gateway (two vertical lines with a horizontal bar across the top, like a simple archway frame). No subtitle text, no stats, no version, no dashboard, no other elements. Just the wordmark, the icon, and the subtle grid. Editorial minimalism, very flat, very refined. Pure black, white, and one subtle orange accent dot somewhere tiny. No gradients, no clouds, no purple." \
  docs/assets/banner.png \
  --model fal-ai/nano-banana-2 --width 2100 --height 900

fal returned 1584x672 (closest 21:9 it would serve). File is 428 KB.

Other variations tried

• Diamond icon: clean but the diamond was too small and felt less distinctive than the archway
• Bracket monogram >OG<: the grid was rendered as a tight marquee-style box around it which felt too cramped
• Archway (this one): the gateway-shape icon is the most semantically appropriate