Mail: account cards, choose which mail apps to show, optional framed webmail

- Mail page redesigned as one card per account (inbox + compose)
- Settings -> Mail apps: tick the apps you use; saved on the server per person
- WEBMAIL_URL shows your own webmail (e.g. Roundcube) inside the Mail tab; provider shortcuts one tap away
- README: Roundcube setup and framing headers

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -19,6 +19,7 @@ services:
       AUDIOBOOKS_SSO_SECRET: ${AUDIOBOOKS_SSO_SECRET:-}
       AUDIOBOOKS_SSO_URL: ${AUDIOBOOKS_SSO_URL:-}
       VERSE_URL: ${VERSE_URL:-https://versebyversewithnate.us/admin}
+      WEBMAIL_URL: ${WEBMAIL_URL:-}
       PODCAST_URL: ${PODCAST_URL:-https://podcast.necloud.us/}
       ONLYOFFICE_JWT_SECRET: ${ONLYOFFICE_JWT_SECRET:-}    # same value as the OnlyOffice server's JWT secret
       PUBLIC_URL: ${PUBLIC_URL:-}                           # e.g. https://hub.necloud.us (OnlyOffice posts saved edits here)