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/cli/wsserve/command.go

@@ -0,0 +1,89 @@
+package wsserve
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"os/signal"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"git.avsdev.uk/Go/job-search/internal/cli"
+	"git.avsdev.uk/Go/job-search/internal/websocket"
+	"git.avsdev.uk/Go/job-search/internal/websocket/tcpserver"
+	"github.com/spf13/cobra"
+)
+
+func NewCommand(opts *cli.Options) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "wsserve",
+		Short: "Run JobSearch TCP Websocket server",
+		PersistentPreRun: func(cmd *cobra.Command, args []string) {
+			slog.Debug("wsserve.PersistentPreRun")
+		},
+		PersistentPostRun: func(cmd *cobra.Command, args []string) {
+			slog.Debug("wsserve.PersistentPostRun")
+		},
+		RunE: func(cmd *cobra.Command, args []string) error {
+			slog.Debug("wsserve.Run")
+
+			addrOverride, _ := cmd.Flags().GetString("listen")
+			hostOverride, _ := cmd.Flags().GetString("host")
+			portOverride, _ := cmd.Flags().GetInt("port")
+
+			if addrOverride != "" {
+				listenParts := strings.Split(addrOverride, ":")
+				if len(listenParts) != 2 {
+					return fmt.Errorf(
+						"--listen should be in the format of 127.0.0.1:9393",
+					)
+				}
+				i, err := strconv.Atoi(listenParts[1])
+				if err != nil {
+					return fmt.Errorf("Failed to parse --listen port: %w", err)
+				}
+				hostOverride = listenParts[0]
+				portOverride = i
+			}
+
+			conf, err := opts.RunSetup(cmd, true, true)
+			if err != nil {
+				return fmt.Errorf("no configuration loaded (%w)", err)
+			}
+
+			if portOverride != 0 {
+				conf.Server.Port = portOverride
+			}
+			if hostOverride != "" {
+				conf.Server.Host = hostOverride
+			}
+
+			// ctx is cancelled on the first SIGINT (Ctrl+C) or SIGTERM.
+			ctx, stop := signal.NotifyContext(
+				context.Background(), os.Interrupt, syscall.SIGTERM,
+			)
+			defer stop()
+
+			// After the first signal, restore default signal handling so a second
+			// Ctrl+C force-kills the process if graceful shutdown hangs.
+			go func() {
+				<-ctx.Done()
+				stop()
+			}()
+
+			hub := websocket.NewHub(conf.Server.WebSocket, slog.Default())
+			svr := tcpserver.New(&conf.Server, hub, slog.Default())
+
+			return svr.Run(ctx)
+		},
+	}
+	cmd.Flags().String("listen", "", "listen address (default from config, 127.0.0.1:9393)")
+	cmd.Flags().String("host", "", "listen address (default from config, 127.0.0.1)")
+	cmd.Flags().Int("port", 0, "listen address (default from config, 9393)")
+	cmd.Flags().Bool("foreground", false, "run in the foreground")
+	cmd.MarkFlagsMutuallyExclusive("listen", "host")
+	cmd.MarkFlagsMutuallyExclusive("listen", "port")
+	return cmd
+}