Add per-domain DKIM signing, admin console TLS, log rotation, and resolver timeout scoping

- DKIM signing was hardcoded to one domain; now keyed per-domain off
  the sending address, fixing mail for every domain but the original.
- Admin console (port 1027) is now TLS-wrapped instead of plaintext.
- barantmail.log now rotates by size (config-driven) instead of
  growing unbounded (previously hit 23GB).
- ResolverThreadScope.h: a <setenv> scoping fix for name resolution
  inside a <try> block that previously did not survive its own
  container.
- IMAPArgs.cpp: fixed "UID STORE 1:*" wrongly requiring UID 1 to
  exist, which silently made empty-folder operations delete nothing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

SendMail.h

@@ -4,6 +4,7 @@
 #include "DKIMSigner.h"
 #include "File.h"
 #include "MString.h"
+#include <map>
 #include <string>
 #include <vector>
 
@@ -41,13 +42,17 @@ namespace mail {
    class SendMail {
 
     public:
-      // dkimSigner is optional (nullptr = don't sign) and not owned -
-      // the caller keeps it alive for as long as any SendMail built
-      // from it might still be sending (a shared signer is fine to
-      // reuse across many messages; it holds no per-message state).
+      // dkimSigners is optional (nullptr = don't sign anything) and not
+      // owned - the caller keeps both it and every DKIMSigner it points
+      // to alive for as long as any SendMail built from it might still
+      // be sending (shared, reusable across many messages; a signer
+      // holds no per-message state). Keyed by domain (matching a
+      // sender address's own domain, case-sensitive exact match, via
+      // domainOf() on `from`) - a domain with no entry just goes out
+      // unsigned, same as dkimSigners being nullptr entirely.
       SendMail(std::string hostName, std::string sendLogPath, std::string messageId,
                coreutils::MString from, coreutils::MString recipient, coreutils::MString mailData,
-               DKIMSigner *dkimSigner = nullptr);
+               std::map<std::string, DKIMSigner*> *dkimSigners = nullptr);
 
       /// Blocking. Returns true if some MX host for the recipient's
       /// domain accepted the message, false if DNS resolution or every
@@ -68,7 +73,7 @@ namespace mail {
       coreutils::MString from;
       coreutils::MString recipient;
       coreutils::MString mailData;
-      DKIMSigner *dkimSigner;
+      std::map<std::string, DKIMSigner*> *dkimSigners;
 
    };