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.

SECURITY.md

@@ -22,13 +22,13 @@ Please include as much of the following as you can:
 - A description of the vulnerability and its potential impact
 - Steps to reproduce, or a proof-of-concept
 - The version/commit of ihasmail affected
-- The version of Stalwart Mail Server you were testing against, if relevant
-- Whether the issue is in ihasmail itself, in how it talks to Stalwart over JMAP, or in a dependency
+- The version of the mail server you were testing against, if relevant
+- Whether the issue is in the webmail itself, in how it talks to the mail server over JMAP, or in a dependency
 
 ### What to Expect
 
 - **Acknowledgment:** You should receive a response within a few days confirming the report was received.
-- **Assessment:** The issue will be triaged and its severity assessed. Because ihasmail holds no data of its own and relies entirely on Stalwart's store over JMAP, some reports may need to be routed to or coordinated with the [Stalwart Mail Server](https://github.com/stalwartlabs/mail-server) project if the root cause lives there rather than in ihasmail's client code.
+- **Assessment:** The issue will be triaged and its severity assessed. Because ihasmail holds no data of its own and relies entirely on the mail server's store over JMAP, some reports may need to be routed to or coordinated with the mail server's own project if the root cause lives there rather than in ihasmail's client code.
 - **Fix & disclosure:** Once a fix is ready, a new release will be published. We'll coordinate with you on public disclosure timing and credit, if you'd like to be credited.
 
 ### Scope
@@ -42,9 +42,9 @@ In scope:
 
 Out of scope (please report upstream instead):
 
-- Vulnerabilities in Stalwart Mail Server itself — report those to the [Stalwart project](https://github.com/stalwartlabs/mail-server)
+- Vulnerabilities in the INBUXA mail server itself: report those to the mail server's own project
 - Vulnerabilities in third-party libraries with no demonstrated impact on ihasmail
-- Issues requiring physical access to a user's device or an already-compromised Stalwart instance
+- Issues requiring physical access to a user's device or an already-compromised mail server
 
 ## Disclosure Policy