fix(sub): resolve legacy socket fallback fronts on PostgreSQL too

The socket-front lookup filtered and extracted settings.fallbacks with
SQLite's json_valid, JSON_TYPE and json_extract, which PostgreSQL does
not have, so on PostgreSQL the statement failed and a legacy @socket
child never got its front's address and security in its links.

The lookup now selects the inbounds whose settings mention fallbacks and
parses them in Go, which works on both databases and still skips an
inbound whose settings do not decode.

internal/sub/host_sub_test.go

@@ -2048,8 +2048,10 @@ func TestSub_LegacyFallbackMasterLookedUpOncePerRequest(t *testing.T) {
 
 	scans := 0
 	count := func(tx *gorm.DB) {
-		if strings.Contains(tx.Statement.SQL.String(), "$.fallbacks") {
+		for _, v := range tx.Statement.Vars {
-			scans++
+			if v == "%fallbacks%" {
+				scans++
+			}
 		}
 	}
 	_ = db.Callback().Query().After("gorm:query").Register("test:count_front_scans", count)

internal/sub/service.go

@@ -3607,20 +3607,22 @@ func (s *SubService) socketFront(key socketFrontKey) *model.Inbound {
 			Listen         string
 			Port           int
 			StreamSettings string
-			Fallbacks      string
+			Settings       string
 		}
-		// json_valid keeps one inbound with unreadable settings from failing the
+		// Parsed here, not with SQL JSON functions, so the lookup works on PostgreSQL too and one
-		// whole statement and hiding every front.
+		// inbound with unreadable settings cannot hide every front.
 		if err := database.GetDB().Model(model.Inbound{}).
-			Select("node_id, listen, port, stream_settings, json_extract(settings, '$.fallbacks') AS fallbacks").
+			Select("node_id, listen, port, stream_settings, settings").
-			Where("CASE WHEN json_valid(settings) THEN JSON_TYPE(settings, '$.fallbacks') END = 'array'").
+			Where("settings LIKE ?", "%fallbacks%").
 			Order("id ASC").Scan(&fronts).Error; err != nil {
 			return nil
 		}
 		for _, front := range fronts {
-			var fallbacks []any
+			var parsed struct {
-			_ = json.Unmarshal([]byte(front.Fallbacks), &fallbacks)
+				Fallbacks []any `json:"fallbacks"`
-			for _, fallback := range fallbacks {
+			}
+			_ = json.Unmarshal([]byte(front.Settings), &parsed)
+			for _, fallback := range parsed.Fallbacks {
 				rule, _ := fallback.(map[string]any)
 				dest, _ := rule["dest"].(string)
 				k := socketFrontKey{node: nodeKeyOf(front.NodeID), dest: dest}