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).

POP3Server.h

@@ -2,7 +2,11 @@
 #define __POP3Server_h__
 
 #include "TCPServer.h"
+#include "TLSInfo.h"
 #include "Exception.h"
+#include "MailFileSystem.h"
+#include "POP3Session.h"
+#include "__POP3_CAPA.h"
 #include "__POP3_DELE.h"
 #include "__POP3_LAST.h"
 #include "__POP3_LIST.h"
@@ -14,6 +18,7 @@
 #include "__POP3_RSET.h"
 #include "__POP3_STAT.h"
 #include "__POP3_TOP.h"
+#include "__POP3_UIDL.h"
 #include "__POP3_USER.h"
 
 namespace mail {
@@ -21,8 +26,11 @@ namespace mail {
    class POP3Server : public core::TCPServer {
 
     public:
-      POP3Server(core::EPoll &epoll, std::string hostName, MailFileSystem &mailFileSystem, core::IPAddress ipAddress)
-	: TCPServer(epoll, ipAddress, " ", 10, "POP3 Server"), mailFileSystem(mailFileSystem), hostName(hostName) {	   
+      POP3Server(core::EPoll &epoll, std::string hostName, MailFileSystem &mailFileSystem,
+                 core::IPAddress ipAddress, core::TLSInfo *tlsInfo)
+	: TCPServer(epoll, ipAddress, tlsInfo, " ", 10, "POP3 Server"), mailFileSystem(mailFileSystem), hostName(hostName) {
+         // RFC 2449: was not registered at all before.
+         commands.add(_pop3_capa, "CAPA");
          commands.add(_pop3_dele, "DELE");
          commands.add(_pop3_last, "LAST");
          commands.add(_pop3_list, "LIST");
@@ -34,13 +42,24 @@ namespace mail {
          commands.add(_pop3_rset, "RSET");
          commands.add(_pop3_stat, "STAT");
          commands.add(_pop3_top, "TOP");
+         commands.add(_pop3_uidl, "UIDL");
          commands.add(_pop3_user, "USER");
       }      
 
       MailFileSystem &mailFileSystem;
       std::string hostName;
-      
+
+      // Same reasoning as IMAPServer's own override - without it every
+      // accepted connection gets a plain TCPSession, POP3Session's
+      // greeting never fires, and POP3Command's (POP3Session &)session
+      // casts are undefined behavior against an object that was never
+      // actually a POP3Session.
+      POP3Session *getSocketAccept(core::EPoll &ePoll) override {
+         return new POP3Session(ePoll, *this);
+      }
+
     private:
+      __POP3_CAPA _pop3_capa;
       __POP3_DELE _pop3_dele;
       __POP3_LAST _pop3_last;
       __POP3_LIST _pop3_list;
@@ -52,6 +71,7 @@ namespace mail {
       __POP3_RSET _pop3_rset;
       __POP3_STAT _pop3_stat;
       __POP3_TOP _pop3_top;
+      __POP3_UIDL _pop3_uidl;
       __POP3_USER _pop3_user;
       
    };