Polish header sizing + refined Inter kicker tags

- Header logo sized up to read clearly (54px desktop / 46px mobile, bars to match).
- Self-host Inter (variable, latin) — no external font calls — and use it for
  the category tags as uppercase Light (300) kickers with tight tracking, for a
  clean, polished label feel.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/app.css

@@ -1,3 +1,13 @@
+/* Inter (variable, latin) — self-hosted, no external font calls. Used for
+   refined UI labels / kicker tags. The weight axis (100–900) is free to tune. */
+@font-face {
+  font-family: "Inter";
+  src: url("/fonts/inter-latin-wght-normal.woff2") format("woff2");
+  font-weight: 100 900;
+  font-style: normal;
+  font-display: swap;
+}
+
 /* Upbeat Bytes calm design system.
    Sand, sea, and sun: warm paper surfaces, a vivid-azure accent, gold highlight,
    a serif voice for headlines, strong readable contrast, generous space.
@@ -16,6 +26,7 @@
 
   --serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, "Times New Roman", serif;
   --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
+  --label: "Inter", var(--sans);
 
   --maxw: 880px;
   --radius: 16px;