feat: Add /force-encryption command and update message handling

Implement /force-encryption command to configure forced encryption
settings with on|off and policy resend-to-confirm|block options.

The changes enhance user experience by clarifying encryption requirements
and providing actionable commands. Users can now press Enter again to
confirm unencrypted messages in resend-to-confirm mode.

src/config/preferences.c

@@ -1792,6 +1792,8 @@ _get_group(preference_t pref)
     case PREF_OUTGOING_STAMP:
     case PREF_INCOMING_STAMP:
     case PREF_MOOD:
+    case PREF_FORCE_ENCRYPTION:
+    case PREF_FORCE_ENCRYPTION_MODE:
         return PREF_GROUP_UI;
     case PREF_STATES:
     case PREF_OUTTYPE:
@@ -2150,6 +2152,10 @@ _get_key(preference_t pref)
         return "strophe.sm.enabled";
     case PREF_STROPHE_SM_RESEND:
         return "strophe.sm.resend";
+    case PREF_FORCE_ENCRYPTION:
+        return "force-encryption.enabled";
+    case PREF_FORCE_ENCRYPTION_MODE:
+        return "force-encryption.policy";
     default:
         return NULL;
     }
@@ -2204,6 +2210,7 @@ _get_default_boolean(preference_t pref)
     case PREF_STROPHE_SM_RESEND:
         return TRUE;
     case PREF_PGP_PUBKEY_AUTOIMPORT:
+    case PREF_FORCE_ENCRYPTION:
     default:
         return FALSE;
     }
@@ -2310,6 +2317,8 @@ _get_default_string(preference_t pref)
         return "0";
     case PREF_DBLOG:
         return "on";
+    case PREF_FORCE_ENCRYPTION_MODE:
+        return "resend-to-confirm";
     default:
         return NULL;
     }

src/config/preferences.h

@@ -187,6 +187,8 @@ typedef enum {
     PREF_STROPHE_SM_RESEND,
     PREF_VCARD_PHOTO_CMD,
     PREF_STATUSBAR_TABMODE,
+    PREF_FORCE_ENCRYPTION,
+    PREF_FORCE_ENCRYPTION_MODE
 } preference_t;
 
 typedef struct prof_alias_t