feat(landing): switch heading font to Block Blueprint

Replace Pixelify Sans with Block Blueprint as the heading font (theme.headFont).
Block Blueprint isn't on Google Fonts, so it's vendored straight from 1001fonts
(License: 1001Fonts Free For Personal Use — fine for this private friends'
server) as a TTF, with a hand-written @font-face appended to fonts.css. The
vendor step is added to fetch-fonts.sh (runs after the Google rewrite so it
survives re-runs). Pixelify stays available as a HEAD_FONTS option + the
hard-coded fallback.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

landing/src/data/site.ts

@@ -120,12 +120,12 @@ export const site = {
   // Design knobs (replace the design's in-browser TweaksPanel). Baked at build.
   //   mood:     "grass" | "nether" | "end"
   //   hero:     "centered" | "split" | "spotlight"
-  //   headFont: "pixelify" | "8bit" | "silkscreen"
+  //   headFont: "blockblueprint" | "pixelify" | "8bit" | "silkscreen"
   //   dust:     floating pixel particles in the hero
   theme: {
     mood: "grass",
     hero: "centered",
-    headFont: "pixelify",
+    headFont: "blockblueprint",
     dust: true,
   },
 
@@ -216,6 +216,7 @@ export const LITERALS = {
 
 // Head-font CSS stacks, keyed by theme.headFont.
 export const HEAD_FONTS: Record<string, string> = {
+  blockblueprint: "'Block Blueprint', system-ui, sans-serif",
   pixelify: "'Pixelify Sans', system-ui, sans-serif",
   "8bit": "'Press Start 2P', monospace",
   silkscreen: "'Silkscreen', system-ui, sans-serif",