Add real IMAP4rev1/POP3 implementations, DKIM/DMARC/SPF, SpamAssassin delivery hook

IMAP (RFC 3501): LOGIN through UID, previously all stubs except
CAPABILITY/LOGOUT/a partial APPEND. Multi-folder support with per-folder
UID/flag indexing (new MailFolder class, backed by .uidvalidity/.uidnext/
.imapindex sidecar files), ENVELOPE support (new MessageHeaders class:
header parsing, address-list parsing, IMAP quoting), and shared
cursor-based argument parsing (new IMAPArgs class: sequence sets, flag
lists, dates, folder-name normalization, and path-traversal protection
via isValidFolderName - a bare ".." folder name would otherwise resolve
into a sibling user's mailbox directory).

POP3 (RFC 1939): USER through QUIT, previously only CAPA. Added UIDL.
POP3 handlers use cursor-based parsing throughout rather than indexed
access - ZString's copy constructor doesn't copy its `list` field, and
POP3's dispatch passes the request by value, so indexed access into a
copy was silently reading nothing.

SMTP: DMARC evaluation added to the DATA-terminator path (DKIM
verification + alignment/policy, Authentication-Results header,
conditional rejection matching RFC 7489 6.3's p=reject + sampled pct=).
AUTH LOGIN now handles RFC 4954's optional inline initial response
(e.g. Python smtplib's "AUTH LOGIN <base64>" in one line) instead of
only the exact three-line form. Outbound relay now forces IPv4
(AF_INET) instead of AF_UNSPEC - this server's IPv4 has a correct PTR
record and SPF coverage, its IPv6 doesn't, and Gmail was rejecting
outbound mail with 550 5.7.25 as a result.

Delivery pipeline: local delivery now runs the message through
SpamAssassin (new SpamAssassinFilter class, speaking spamd's PROCESS
protocol directly over a raw socket - fails open/delivers unscanned if
spamd is unreachable) instead of a plain hardlink, since scanning can
tag/modify content.

BARANTMailConfig: extracted config loading into its own class.

compile: (see individual file changes - build script adjustments to
match the above).

Deliberately excluded from this commit: barantmail.log/
barantmail-service.log (operational logs, not source - barantmail.log
in particular was the runaway 55GB/12.9GB file from a busy-loop bug
fixed separately in ServerCore) and barantmail.cfg (this server's own
live deployment config, matching how APIServer's equivalent
config also stays untracked).

__SMTP_EHLO.cpp

@@ -5,12 +5,27 @@ namespace mail {
 
    int __SMTP_EHLO::processCommand(coreutils::ZString &request, SMTPSession &session, SMTPServer &server) {
 
+      // RFC 5321 4.1.1.1 requires a domain/address-literal argument -
+      // request[1] on a bare "EHLO" with none would have been an
+      // out-of-bounds read on the split list (ZString::operator[] does
+      // no bounds checking), not a graceful rejection.
+      if (request.getList().size() < 2) {
+         session.out << "501 Syntax error: EHLO requires a domain/address-literal argument" << CRLF;
+         return 1;
+      }
+
       session.clientDomainName = request[1];
-//      std::cout << "{" << session.clientDomainName << "}" << std::endl;
       session.out << "250-" << server.hostName << CRLF;
-      //  cout << "250-STARTTLS" << CRLF;
-      //  cout << "250-PIPELINING" << CRLF;
-      //  cout << "250-8BITMIME" << CRLF;
+      // Both already true of this implementation, not just advertised
+      // hopefully: multiple pipelined command lines arriving in one TCP
+      // segment are already handled correctly (TCPSocket::onDataReceived
+      // loops over every complete line it has buffered before returning,
+      // not just the first), and message bodies are stored byte-for-byte
+      // with no 7-bit stripping anywhere in this codebase.
+      session.out << "250-PIPELINING" << CRLF;
+      session.out << "250-8BITMIME" << CRLF;
+      // Enforced by __SMTP_DATA.cpp while accumulating the body.
+      session.out << "250-SIZE " << (long)SMTPServer::maxMessageSize << CRLF;
       session.out << "250-AUTH LOGIN" << CRLF;
       session.out << "250 HELP" << CRLF;
       session.state = READY;