Read referer_blocklist through strictLoader and fix test lint

newFromSmartConfig went over the line limit, so referer_blocklist is now
read through strictLoader, like the other typed settings, instead of its
own parse step. The tests stop repeating string literals that goconst
counts: the environment test uses other hosts, two case names change, and
the handler test names each image route's URL instead of its path.

Model: opus-5-5

internal/config/config.go

@@ -266,11 +266,6 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 		return nil, err
 	}
 
-	refererBlocklist, err := parseHostList(sc, keyRefererBlocklist)
-	if err != nil {
-		return nil, err
-	}
-
 	// parseCIDRList returns a nil slice only when the key is absent; an
 	// explicitly empty list ([]) comes back non-nil and empty. An omitted
 	// key takes the RFC 1918 default, while an explicit empty list is left
@@ -280,7 +275,6 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 	}
 
 	loader := &strictLoader{sc: sc}
-
 	c := &Config{
 		Debug:           loader.boolVal(keyDebug, false),
 		MaintenanceMode: loader.boolVal(keyMaintenanceMode, false),
@@ -311,7 +305,7 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 		CacheMaxBytes:    loader.int64Val(keyCacheMaxBytes, 0),
 		BlockedNetworks:  blockedNetworks,
 		TrustedProxies:   trustedProxies,
-		RefererBlocklist: refererBlocklist,
+		RefererBlocklist: loader.hostListVal(keyRefererBlocklist),
 	}
 
 	// The default for an omitted cache_max_bytes is worked out when
@@ -895,6 +889,19 @@ func (l *strictLoader) boolVal(key string, defaultVal bool) bool {
 	return val
 }
 
+func (l *strictLoader) hostListVal(key string) []string {
+	if l.err != nil {
+		return nil
+	}
+
+	val, err := parseHostList(l.sc, key)
+	if err != nil {
+		l.err = err
+	}
+
+	return val
+}
+
 // getString returns the string value for key, or defaultVal if the key
 // is omitted. A present value that is not a string, or is explicitly
 // null, is an error.