Digest masthead: use the real logo as a hosted PNG

Per Codex — cleanest, most brand-consistent option. Rasterized logo.svg to a
small transparent logo-email.png (360px wide, shown at 180px for retina), served
at /logo-email.png. alt="Upbeat Bytes" keeps the brand if a client blocks
images. SVG isn't email-safe; a hosted PNG is the standard approach.

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

goodnews/digest.py

@@ -104,10 +104,10 @@ 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">'
-        # Two-tone lowercase wordmark echoing the logo (azure + navy), tight-tracked.
-        '<div style="font-family:\'Helvetica Neue\',Arial,sans-serif;font-size:32px;font-weight:700;'
-        'letter-spacing:-0.045em;margin:0;line-height:1">'
-        '<span style="color:#0083ad">upbeat</span> <span style="color:#002772">bytes</span></div>'
+        # The real logo as a small hosted PNG (SVG isn't email-safe); alt text
+        # keeps the brand when a client blocks remote images.
+        f'<img src="{base}/logo-email.png" alt="Upbeat Bytes" width="180" '
+        'style="display:block;border:0;outline:none;text-decoration:none;height:auto;margin:0 0 2px">'
         '<div style="font-size:11px;letter-spacing:0.14em;text-transform:uppercase;color:#0083ad;'
         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">'