feat(fonts): self-host interface fonts as vendored latin woff2

Replace Google Fonts CDN delivery of the four UI typefaces (Inter,
Space Grotesk, Space Mono, Syne) with latin-subset woff2 vendored into
app/assets/fonts and wired via a hand-authored @font-face stylesheet.
Variable faces keep wght (Inter also opsz). Vite content-hashes the
binaries for immutable caching.

src/app/styles/app.css

@@ -1,5 +1,6 @@
 @import "tailwindcss";
 @import "tw-animate-css";
+@import "./fonts.css";
 
 @variant dark (&:where(.dark, .dark *));