polish: clean header, unified IBM Plex Sans typography

- Remove Daily Briefing title and live indicator from header
- Center clock prominently in header bar
- Switch all section headings to IBM Plex Sans (matching card titles)
- Remove unused Outfit font import

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

web/tailwind.config.js

@@ -45,7 +45,7 @@ export default {
         },
       },
       fontFamily: {
-        serif: ['"Instrument Serif"', "Georgia", "serif"],
+        serif: ['"IBM Plex Sans"', "system-ui", "sans-serif"],
         sans: ['"IBM Plex Sans"', "system-ui", "sans-serif"],
         mono: ['"IBM Plex Mono"', "Menlo", "monospace"],
       },