Deferred: pixel-art logo/favicon redraw + social assets

[Sealjay]

Problems

• public/favicon.svg hardcodes hex (#0f3c46/#d5a425/#f3e9d2) and is a generic, non-pixel-art castle that does not match the 8-bit brand (a standalone SVG cannot read tokens.css, so brand hex must be baked in deliberately).
• src/assets/str-logo.png is 1024×1024 and SQUARE, but Seo.astro declares og:image:width=1200 / og:image:height=630 → distorted/cropped social cards. It is also wired as apple-touch-icon at full 1024px.

Deliverables

• Pixel-art favicon SVG matching CastleSceneRetro (crispEdges, 2px stroke, brand palette baked in).
• Dedicated 1200×630 OG image.
• 180×180 apple-touch-icon.
• Small raster favicon fallback (e.g. 32×32).
• Update Base.astro / Seo.astro references accordingly.

Out of scope here

Not part of feat/design-review-overhaul.