Enable stream management and CSI for mobile clients.

Conversations re-authenticated every 5-10 minutes (138 full logins in
two days) because no XEP-0198 module was loaded. Each reconnect re-ran
its OMEMO bootstrap and republished the PEP device list built from a
partial fetch, which dropped the desktop client's device id from the
list. Senders then encrypted to nobody, and Gajim showed "could not be
decrypted" until it reconnected and re-added itself.

smacks lets the session resume across network blips, csi_simple keeps
backgrounded clients quiet. Both ship with Prosody 0.12.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

data/prosody/configuration/prosody.cfg.lua

@@ -25,6 +25,17 @@ modules_enabled = {
 	"register";
 	"mam";
 
+	-- Mobile-friendly sessions. smacks (XEP-0198) lets a client resume a
+	-- dropped connection instead of re-authenticating; csi_simple (XEP-0352)
+	-- lets the server hold back unimportant traffic for backgrounded clients.
+	-- Without smacks the phone re-authenticated every few minutes, and each
+	-- reconnect re-ran Conversations' OMEMO bootstrap, which republished the
+	-- PEP device list without the devices it had not managed to fetch. That
+	-- silently dropped the desktop client from the list, so messages were
+	-- encrypted to nobody and could never be decrypted there.
+	"smacks";
+	"csi_simple";
+
 	-- Admin interface
 	"admin_adhoc";