Brand consistency: emails say "upbeatBytes" (From + digest body)

Per the brand-name standard (camelCase, one word). Updated the SMTP From default and
the digest email body/subject strings. Live env From values (auth.env + goodnews.env)
updated to match. (Web/OG brand strings in share.py + app.html are the remaining sweep.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

goodnews/email_send.py

@@ -24,7 +24,7 @@ def _cfg() -> dict:
         "port": int(os.environ.get("GOODNEWS_SMTP_PORT", "587")),
         "user": os.environ.get("GOODNEWS_SMTP_USER", ""),
         "password": os.environ.get("GOODNEWS_SMTP_PASSWORD", ""),
-        "sender": os.environ.get("GOODNEWS_SMTP_FROM", "Upbeat Bytes <hello@upbeatbytes.com>"),
+        "sender": os.environ.get("GOODNEWS_SMTP_FROM", "upbeatBytes <hello@upbeatbytes.com>"),
         # Where a reader's reply should land; falls back to the From address.
         "reply_to": os.environ.get("GOODNEWS_REPLY_TO_EMAIL", ""),
     }