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).

__POP3_PASS.cpp

@@ -0,0 +1,41 @@
+#include "__POP3_PASS.h"
+#include "POP3Server.h"
+
+namespace mail {
+
+   int __POP3_PASS::processCommand(coreutils::ZString request, POP3Session &session, POP3Server &server) {
+      request.skipWhitespace();
+      // Deliberately the rest of the line, not just the first
+      // whitespace-delimited token - RFC 1939 4's PASS <string> may
+      // contain any character except CR/LF, spaces included. (A known,
+      // documented gap of this same shape exists nowhere else in this
+      // codebase for POP3, since every other POP3 argument is a bare
+      // number or single atom that's never expected to contain a
+      // space.)
+      coreutils::ZString passArg = request.unparsed();
+
+      if (session.userName.empty()) {
+         session.out << "-ERR USER required first" << CRLF;
+         return 1;
+      }
+      if (passArg.getLength() == 0) {
+         session.out << "-ERR Usage: PASS <password>" << CRLF;
+         return 1;
+      }
+
+      coreutils::ZString userNameZ(session.userName);
+      if (!server.mailFileSystem.checkPassword(userNameZ, passArg)) {
+         session.out << "-ERR Authentication failed" << CRLF;
+         session.userName.clear();
+         return 1;
+      }
+
+      coreutils::ZString userNameZ2(session.userName);
+      std::string mailboxPath = server.mailFileSystem.getFolderPath(userNameZ2, "Inbox").str();
+      session.mailbox.load(mailboxPath);
+      session.authenticated = true;
+      session.out << "+OK Logged in" << CRLF;
+      return 1;
+   }
+
+}