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).

MailFileSystem.h

@@ -5,6 +5,7 @@
 # include <sys/types.h>
 # include <sys/stat.h>
 # include <unistd.h>
+# include <vector>
 
 namespace mail {
 
@@ -18,10 +19,31 @@ namespace mail {
       std::vector<coreutils::MString> getAliasMailboxes(coreutils::ZString &alias);
       coreutils::ZString& getMailPath();
       coreutils::ZString& getQueuePath();
+      coreutils::ZString& getSendLogPath();
+
+      // Shared by every protocol's login (SMTP AUTH LOGIN, IMAP LOGIN,
+      // POP3 USER/PASS) so there is exactly one place that reads
+      // <mailbox>/.password and compares it - previously
+      // __SMTP_AUTH::authLogin() carried this logic alone, and IMAP/POP3
+      // login would otherwise have needed their own copies. Still a
+      // plaintext file comparison (a separately tracked, pre-existing
+      // gap) - not something this change fixes, just no longer
+      // triplicated.
+      bool checkPassword(coreutils::ZString &userName, coreutils::ZString &password);
+
+      // Folder names (Inbox/Spam/Trash/anything CREATEd) as immediate
+      // subdirectories of a mailbox's own directory - used by IMAP
+      // LIST/LSUB/SELECT/CREATE/DELETE/RENAME to enumerate and validate
+      // folders without each command re-implementing the same
+      // directory scan and dotfile-skipping rule.
+      std::vector<coreutils::MString> listFolders(coreutils::ZString &mailbox);
+      coreutils::MString getFolderPath(coreutils::ZString &mailbox, std::string folder);
+      bool ifFolderExists(coreutils::ZString &mailbox, std::string folder);
 
     private:
       coreutils::ZString &mailPath;
       coreutils::MString queuePath;
+      coreutils::MString sendLogPath;
       struct stat statbuf;
 
    };