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.

server/src/adminurl.test.ts

@@ -14,16 +14,16 @@ writeFileSync(
     "Linked.Test.": { url: "https://mail.linked.test", adminUrl: "https://admin.linked.test/" },
   }),
 );
-process.env.STALWART_URL = "https://default.example";
-process.env.STALWART_ADMIN_URL = "https://admin.default.example/";
-process.env.STALWART_SERVERS_FILE = file;
+process.env.MAIL_SERVER_URL = "https://default.example";
+process.env.ADMIN_URL = "https://admin.default.example/";
+process.env.MAIL_SERVERS_FILE = file;
 
 const { adminPrefixFrom, adminUrlFor, advertisedOrigin, upstreamFor } = await import("./upstream.js");
 const { config, parseStalwartServers } = await import("./config.js");
 
 /**
- * Where the dashboard's "Open Stalwart admin" points. STALWART_URL is how this
- * server reaches Stalwart; STALWART_ADMIN_URL is where a browser opens its
+ * Where the dashboard's "Open Stalwart admin" points. MAIL_SERVER_URL is how this
+ * server reaches Stalwart; ADMIN_URL is where a browser opens its
  * administration, and follows the same domain routing.
  */
 test("a servers file entry may name its administration as well as its server, and a note is not a domain", () => {
@@ -67,7 +67,7 @@ test("the origin is the one Stalwart advertises, even when it is reached on a pr
 });
 
 test("the shipped example loads through the parser that reads it", () => {
-  const example = new URL("../../stalwart-servers.example.json", import.meta.url);
+  const example = new URL("../../mail-servers.example.json", import.meta.url);
   const parsed = parseStalwartServers(JSON.parse(readFileSync(example, "utf8")), "example");
   assert.ok(Object.keys(parsed.urls).length > 0);
   assert.ok(!("_comment" in parsed.urls));