Added websocket hub for handling websocket clients, with a wsserve command

which runs a plain TCP server for receiving websocket hub clients, with
server config, CSRF and rate limit middleware.

- internal/websocket: Hub pushing messages to WebSocket clients (ServeHTTP,
  example.com/ws upgrade with optional CSRF check) and plain TCP clients (ServeTCP,
  newline-delimited JSON envelopes); ping/pong keepalive, per-client message
  rate limit, slow consumer handling, graceful Shutdown, debug logging of
  messages sent and received
- internal/websocket/tcpserver: standalone TCP server for a hub, with accept
  back-off, a per-IP connection limit (server.websocket.connection_limit) and
  graceful shutdown
- internal/cli/wsserve: `wsserve` command running the TCP server, with
  --listen/--host/--port overrides
- internal/middleware: keyed token bucket rate limiter, real client IP from
  trusted proxies
- internal/httpx: RFC 9457 problem responses, request IDs in context
- internal/config: server section (host, port, shutdown timeout, rate limiter
  idle TTL, websocket); util.ByteSize settings (e.g. "32KiB"); lists of
  sections as single keys; empty lists stored as nil; isExplicitlySet for
  printLoadedConfig; JobSearchConfigSource renamed to JSCSourcesSource;
  TestSections checks every section's methods
- internal/util: ByteSize, parsed and formatted with go-humanize

internal/config/config.go

@@ -24,9 +24,10 @@ const EtcConfigPath string = "/etc/job-search"
 // JobSearchConfig is the application's whole configuration, one field per
 // section. Each field's cfg tag must match the section's JSCK* constant.
 type JobSearchConfig struct {
-	Database  JSCDatabase        `cfg:"database"`
-	Logging   JSCLogging         `cfg:"logging"`
-	Sources   JSCSources         `cfg:"sources"`
+	Database JSCDatabase `cfg:"database"`
+	Logging  JSCLogging  `cfg:"logging"`
+	Server   JSCServer   `cfg:"server"`
+	Sources  JSCSources  `cfg:"sources"`
 }
 
 // LoadDefaultConfig sets Viper's defaults from the configuration's default
@@ -88,6 +89,24 @@ func viperValue(key string, kind reflect.Kind) (value any, ok bool) {
 		return viper.GetInt(key), true
 	case reflect.Bool:
 		return viper.GetBool(key), true
+	case reflect.Slice:
+		// A string, e.g. from an environment variable, is passed on for
+		// SetValue to split on commas; GetStringSlice would split it on
+		// spaces. A list of objects (a list of sections) is passed on as it
+		// is, as GetStringSlice would flatten it.
+		switch v := viper.Get(key).(type) {
+		case string:
+			return v, true
+		case []map[string]any: // as LoadToViper sets it
+			return v, true
+		case []any:
+			if len(v) > 0 {
+				if _, ok := v[0].(map[string]any); ok {
+					return v, true
+				}
+			}
+		}
+		return viper.GetStringSlice(key), true
 	}
 	return nil, false
 }