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).

__IMAP_STORE.cpp

@@ -0,0 +1,80 @@
+#include "__IMAP_STORE.h"
+#include "IMAPArgs.h"
+#include "IMAPServer.h"
+#include <algorithm>
+#include <cctype>
+
+namespace mail {
+
+   namespace {
+      std::string joinFlags(const std::vector<std::string> &flags) {
+         std::string out;
+         for (size_t i = 0; i < flags.size(); ++i) {
+            if (i > 0)
+               out += " ";
+            out += flags[i];
+         }
+         return out;
+      }
+   }
+
+   int storeImpl(coreutils::ZString &request, IMAPSession &session, IMAPServer &server, bool uidMode) {
+      if (session.state != IMAPSession::SELECTED) {
+         session.out << session.tag << " NO No mailbox selected" << CRLF;
+         return 1;
+      }
+      if (session.readOnly) {
+         session.out << session.tag << " NO Mailbox is read-only" << CRLF;
+         return 1;
+      }
+
+      std::vector<uint32_t> uids = IMAPArgs::parseSequenceSet(request, session.mailbox, uidMode);
+
+      coreutils::ZString modeArg = IMAPArgs::nextArgument(request);
+      std::string mode = modeArg.str();
+      bool silent = false;
+      // Strip a trailing ".SILENT" (case-insensitive) before inspecting
+      // the leading +/- sign.
+      if (mode.size() >= 7) {
+         std::string tail = mode.substr(mode.size() - 7);
+         for (char &c : tail)
+            c = std::toupper((unsigned char)c);
+         if (tail == ".SILENT") {
+            silent = true;
+            mode = mode.substr(0, mode.size() - 7);
+         }
+      }
+
+      char sign = mode.empty() ? '=' : mode[0];
+      std::vector<std::string> flags = IMAPArgs::parseFlagList(request);
+
+      for (uint32_t uid : uids) {
+         MailFolder::Message *message = session.mailbox.find(uid);
+         if (!message)
+            continue;
+
+         if (sign == '+')
+            session.mailbox.addFlags(uid, flags);
+         else if (sign == '-')
+            session.mailbox.removeFlags(uid, flags);
+         else
+            session.mailbox.setFlags(uid, flags);
+
+         if (!silent) {
+            uint32_t seqNum = session.mailbox.seq(uid);
+            session.out << "* " << (int)seqNum << " FETCH (FLAGS (" << joinFlags(message->flags) << ")";
+            if (uidMode)
+               session.out << " UID " << (int)uid;
+            session.out << ")" << CRLF;
+         }
+      }
+
+      session.out << session.tag << " OK " << (uidMode ? "UID STORE" : "STORE") << " completed" << CRLF;
+      return 1;
+   }
+
+   int __IMAP_STORE::processCommand(coreutils::ZString &request, IMAPSession &session, IMAPServer &server) {
+      return storeImpl(request, session, server, false);
+   }
+
+}