Digest email: lowercase 'upbeat bytes' masthead + intro spacing/divider

Per user: lowercase masthead to echo the logo's character (kept as text, not an
image — email clients strip SVG and block remote images, so text always renders
and degrades gracefully). More breathing room before the 'Good morning' intro,
and a horizontal divider after it to match the item separators. (Real logo PNG
remains an option if wanted.)

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

goodnews/digest.py

@@ -104,13 +104,14 @@ def build_digest(items: list[dict], brief_date: str, unsub_url: str, base: str |
     html = (
         '<div style="max-width:600px;margin:0 auto;padding:8px 4px;'
         'font-family:-apple-system,Segoe UI,Roboto,Helvetica,Arial,sans-serif;color:#16263a">'
-        '<div style="font-family:Georgia,\'Times New Roman\',serif;font-size:26px;font-weight:700;'
-        'letter-spacing:-0.01em;margin:0">Upbeat Bytes</div>'
+        '<div style="font-family:Georgia,\'Times New Roman\',serif;font-size:30px;font-weight:700;'
+        'letter-spacing:-0.01em;margin:0;color:#16263a">upbeat bytes</div>'
         '<div style="font-size:11px;letter-spacing:0.14em;text-transform:uppercase;color:#0083ad;'
-        f'margin:4px 0 0">Daily Highlights · {escape(weekday)}</div>'
-        '<p style="font-size:15px;line-height:1.5;color:#3b4754;margin:16px 0 24px">'
+        f'margin:5px 0 0">Daily Highlights · {escape(weekday)}</div>'
+        '<p style="font-size:15px;line-height:1.5;color:#3b4754;margin:28px 0 18px">'
         'Good morning. A small, hopeful handful of what’s going right — and there’s always more '
         f'<a href="{base}" style="color:#0083ad;text-decoration:none">waiting on the site</a> when you want it.</p>'
+        '<div style="border-top:1px solid #e8e3d8;margin:0 0 24px"></div>'
         + "".join(blocks)
         + '<p style="font-size:15px;color:#3f7048;margin:8px 0 0">That’s today’s highlights — more good news is '
           f'always <a href="{base}" style="color:#3f7048">waiting on Upbeat Bytes</a>. See you tomorrow.</p>'