docs(design): remove SVG, use PNG logo only

SVG icon is no longer in use. public/logo.png (1024x1024 RGBA) is
the single logo asset. DESIGN.md updated accordingly: SVG snippet
removed, wordmark pattern and <head> references updated to PNG.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

node_modules/tailwindcss/defaultTheme.d.ts

@@ -0,0 +1,4 @@
+import type { Config } from './types/config'
+import { DefaultTheme } from './types/generated/default-theme'
+declare const theme: Config['theme'] & DefaultTheme
+export = theme