AGPL source offer and name cleanup

Every build writes the exact source it was built from, uncommitted work and
new files included, as source.tar.gz next to the app, named after that tree.
Docker builds, which have no git, pack the build context and name it by a
hash of its files. The sign-in page and Settings > About link to it instead of
a repository that can drift.

What users, operators and packagers see no longer names the upstream server:
- interface text, in all nine catalogues, with a token-session line for
  Security;
- server messages;
- the settings, now MAIL_SERVER_URL, MAIL_SERVERS_FILE, ADMIN_URL and
  MAIL_SERVER_FOLLOW_ADVERTISED_URLS, and mail-servers.example.json;
- the Tenants notice, which is gone;
- the README, CONTRIBUTING and SECURITY.

ihasmail's own FEATURES, KNOWN-ISSUES and ROADMAP stay with public ihasmail,
and INBUXA.md is folded into the README.

.env.example

@@ -1,8 +1,8 @@
 # ---- ihasmail server configuration ----
 
-# Base URL of your Stalwart server (scheme + host, no path). ihasmail discovers
-# the JMAP session at <STALWART_URL>/.well-known/jmap.
-STALWART_URL=https://mail.example.com
+# Base URL of your mail server (scheme + host, no path). ihasmail discovers
+# the JMAP session at <MAIL_SERVER_URL>/.well-known/jmap.
+MAIL_SERVER_URL=https://mail.example.com
 
 # Random secret used to derive encryption keys for persisted sessions.
 # Generate with: openssl rand -base64 48
@@ -61,10 +61,10 @@ MAX_UPLOAD_BYTES=52428800
 # Remote-image privacy proxy (Gmail-style). Set to 0 to load remote images directly.
 IMAGE_PROXY=1
 
-# In-app administration, for accounts whose Stalwart role manages accounts and
+# In-app administration, for accounts whose role on the mail server manages accounts and
 # domains. 0 turns it off for everyone: no menu, and the JMAP proxy refuses
-# Stalwart's registry methods beyond an account's own password, app passwords
-# and settings. Stalwart's own admin interface is not affected.
+# the mail server's registry methods beyond an account's own password, app passwords
+# and settings. INBUXA Admin is not affected.
 ADMINISTRATION=1
 
 # Branding
@@ -100,16 +100,16 @@ SOURCE_URL=https://github.com/Coffey-Labs/ihasmail
 # Read once at startup: editing a policy means restarting the container.
 # Docs: https://docs.ihasmail.org/configure/#settings-your-installation-decides
 
-# ---- Several Stalwart servers (optional) ----
+# ---- Several mail servers (optional) ----
 #
-# Choose the upstream by the domain someone signs in with. STALWART_URL above
+# Choose the upstream by the domain someone signs in with. MAIL_SERVER_URL above
 # stays required and stays the default; this only adds domains that go
-# elsewhere. See the shipped stalwart-servers.example.json, and mount it
+# elsewhere. See the shipped mail-servers.example.json, and mount it
 # read-only:
 #
 #   -v /srv/ihasmail/servers.json:/etc/ihasmail/servers.json:ro
 #
-# STALWART_SERVERS_FILE=/etc/ihasmail/servers.json
+# MAIL_SERVERS_FILE=/etc/ihasmail/servers.json
 #
-# An unlisted domain, or a username with no domain, goes to STALWART_URL. A
+# An unlisted domain, or a username with no domain, goes to MAIL_SERVER_URL. A
 # listed domain never falls back. Read once at startup: editing means a restart.