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).

SMTPServer.h

@@ -6,12 +6,15 @@
 # include <filesystem>
 # include "EPoll.h"
 # include "TCPServer.h"
+# include "TLSInfo.h"
 # include "SMTPSession.h"
 # include "MailFileSystem.h"
 # include "__SMTP_AUTH.h"
 # include "__SMTP_DATA.h"
 # include "__SMTP_EHLO.h"
+# include "__SMTP_EXPN.h"
 # include "__SMTP_HELO.h"
+# include "__SMTP_HELP.h"
 # include "__SMTP_MAIL.h"
 # include "__SMTP_NOOP.h"
 # include "__SMTP_QUIT.h"
@@ -20,16 +23,37 @@
 # include "__SMTP_VRFY.h"
 # include "INotify.h"
 # include "SendMail.h"
+# include "DKIMSigner.h"
 namespace mail {
 
    class SMTPServer : public core::TCPServer, public core::INotify {
 
     public:
-      SMTPServer(core::EPoll &ePoll, std::string hostName, MailFileSystem &mailFileSystem, core::IPAddress ipAddress);
+      // watchQueue controls whether this instance watches the mail
+      // queue directory and relays/delivers what lands in it - true by
+      // default for the ordinary single-listener case. Running a
+      // second SMTPServer for a submission/TLS port alongside the
+      // plaintext one needs watchQueue=false on exactly one of the two:
+      // each SMTPServer's own INotify watch is independent, so two
+      // watchers on the same directory would each fire inCreate() for
+      // every queued message, delivering it twice.
+      // dkimSigner is optional (nullptr = outbound mail goes out
+      // unsigned) and not owned - passed straight through to every
+      // SendMail this instance's inCreate() constructs for outbound
+      // relay.
+      SMTPServer(core::EPoll &ePoll, std::string hostName, MailFileSystem &mailFileSystem,
+                 core::IPAddress ipAddress, core::TLSInfo *tlsInfo, bool watchQueue = true,
+                 DKIMSigner *dkimSigner = nullptr);
 
       MailFileSystem &mailFileSystem;
       std::string hostName;
       core::EPoll &ePoll;
+      DKIMSigner *dkimSigner;
+
+      // Advertised via EHLO's "250-SIZE <n>" and enforced by __SMTP_DATA
+      // while accumulating a message body - RFC 1870. 25MB, matching
+      // the limit most real providers (e.g. Gmail) use.
+      static const size_t maxMessageSize = 25 * 1024 * 1024;
 
       SMTPSession * getSocketAccept(core::EPoll &ePoll) override;
       void sessionErrorHandler(std::string errorString, std::stringstream &out);
@@ -41,7 +65,9 @@ namespace mail {
       __SMTP_AUTH _smtp_auth;
       __SMTP_DATA _smtp_data;
       __SMTP_EHLO _smtp_ehlo;
+      __SMTP_EXPN _smtp_expn;
       __SMTP_HELO _smtp_helo;
+      __SMTP_HELP _smtp_help;
       __SMTP_MAIL _smtp_mail;
       __SMTP_NOOP _smtp_noop;
       __SMTP_QUIT _smtp_quit;
@@ -49,7 +75,6 @@ namespace mail {
       __SMTP_RSET _smtp_rset;
       __SMTP_VRFY _smtp_vrfy;
       int wd;
-      std::vector<SendMail> mailQueue;
 
       void processExisting();