Enable mod_mam for persistent direct message archiving

Messages are stored indefinitely in MySQL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

data/prosody/configuration/prosody.cfg.lua

@@ -21,6 +21,7 @@ modules_enabled = {
 	"time";
 	"ping";
 	"register";
+	"mam";
 
 	-- Admin interface
 	"admin_adhoc";
@@ -62,6 +63,9 @@ s2s_require_encryption = true
 -- Authentication
 authentication = "internal_plain"
 
+-- Message archive settings
+archive_expires_after = "never"
+
 -- Certificates directory (global, before VirtualHost)
 certificates = "/etc/prosody/certs"