brand: standardize "Upbeat Bytes" → "upbeatBytes" everywhere

Per the logo + brand: the name is upbeatBytes (camelCase). Swept all user-facing
strings — titles/og:site_name/og:title, logo alt text, share pages (share.py),
emails (email_send), classifier prompt (llm), digest/unsubscribe (api), PWA
manifest, game share text, sign-in, the SPA shell + patch-static-heads (play
title) — plus README/publish.sh and the email test fixture. (SMTP From env was
already upbeatBytes.) Domains (upbeatbytes.com) unchanged. 425 BE + 36 FE green.

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

tests/test_email_reply_to.py

@@ -43,6 +43,6 @@ def test_reply_to_uses_env_inbox(monkeypatch):
 def test_reply_to_falls_back_to_from(monkeypatch):
     _arm(monkeypatch)
     monkeypatch.delenv("GOODNEWS_REPLY_TO_EMAIL", raising=False)
-    monkeypatch.setenv("GOODNEWS_SMTP_FROM", "Upbeat Bytes <hello@upbeatbytes.com>")
+    monkeypatch.setenv("GOODNEWS_SMTP_FROM", "upbeatBytes <hello@upbeatbytes.com>")
     es.send_feedback_reply("reader@x.com", "hi", None, "o")
-    assert _FakeSMTP.last["Reply-To"] == "Upbeat Bytes <hello@upbeatbytes.com>"
+    assert _FakeSMTP.last["Reply-To"] == "upbeatBytes <hello@upbeatbytes.com>"