Digest: enlarge 'From what you follow' heading to a proper section size

It was 11px uppercase — smaller than the 14px links, backwards for a heading.
Now 20px bold ink, clearly a section header above its items.

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

goodnews/digest.py

@@ -169,8 +169,8 @@ def build_digest(items: list[dict], brief_date: str, unsub_url: str, base: str |
     followed_html = ""
     if followed:
         followed_html = (
-            '<div style="font-size:11px;letter-spacing:0.12em;text-transform:uppercase;color:#0083ad;'
-            'margin:8px 0 16px">From what you follow</div>'
+            '<div style="font-size:20px;font-weight:700;letter-spacing:-0.01em;color:#16263a;'
+            'margin:10px 0 18px">From what you follow</div>'
             + "".join(_item_html(it, base) for it in followed)
         )
     html = (