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).

IMAPCommand.cpp

@@ -6,8 +6,39 @@
 namespace mail {
    
    int IMAPCommand::processCommand(coreutils::ZString &request, core::TCPSession &session) {
-      return processCommand(request, (IMAPSession &)session, (IMAPServer &)session.server);	 
+      // session.server is a TCPServer* (pointer) - C-style-casting the
+      // POINTER VALUE directly to a reference type does not dereference
+      // it. Per C++'s reference-cast rules this falls back to
+      // reinterpret_cast<T&>, which for an expression that is not
+      // itself an object is *reinterpret_cast<T*>(&expr) - i.e. it took
+      // the address of the `session.server` POINTER FIELD ITSELF (8
+      // bytes, wherever that field happens to live inside the
+      // TCPSession/IMAPSession object) and read an entire IMAPServer's
+      // worth of memory starting there, not the real IMAPServer object
+      // the pointer actually points to. Confirmed live via gdb: fields
+      // read off the "IMAPServer" this produced were complete garbage
+      // (a null EPoll reference, a socket descriptor of -136794095).
+      // The compiler's own "does not dereference pointer" warning on
+      // this exact line, present on every build all session, was
+      // reporting precisely this. Dereferencing the pointer first
+      // (*session.server, a real TCPServer&) makes the cast to
+      // IMAPServer& a normal, correct base-to-derived downcast.
+      // CommandList::processRequest() (ServerCore) calls request.reset()
+      // right before dispatch - the cursor lands at the true start of
+      // the whole command line, which STILL includes the command word
+      // itself ("LOGIN", "FETCH", ...), not just past it. SMTP handlers
+      // never noticed because they read arguments via request[N] (the
+      // pre-split list, built independently of cursor position) rather
+      // than the cursor - every IMAP handler here parses off the raw
+      // cursor instead (see IMAPArgs.h's own doc comment for why), so
+      // without this, every handler's first nextArgument() call was
+      // reading the command word itself as if it were the first real
+      // argument (confirmed live: LOGIN "user" "pass" produced
+      // userArg=="LOGIN", passArg=="user", with "pass" never read at
+      // all). Discarding it here, once, centrally, is simpler and less
+      // error-prone than every individual handler remembering to do it.
+      request.getTokenExclude(" ");
+      return processCommand(request, (IMAPSession &)session, (IMAPServer &)(*session.server));
    }
 
 }
-