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

cmd/jobsearch/main.go

@@ -28,6 +28,7 @@ import (
 	"git.avsdev.uk/Go/job-search/internal/cli/fetch"
 	"git.avsdev.uk/Go/job-search/internal/cli/migrate"
 	"git.avsdev.uk/Go/job-search/internal/cli/version"
+	"git.avsdev.uk/Go/job-search/internal/cli/wsserve"
 	"github.com/spf13/cobra"
 )
 
@@ -75,6 +76,7 @@ opportunities.
 		config.NewCommand(opts),
 		fetch.NewCommand(opts),
 		migrate.NewCommand(opts),
+		wsserve.NewCommand(opts),
 	)
 
 	return root

cmd/jobsearch/main_test.go

@@ -16,7 +16,7 @@ func TestCommandTree(t *testing.T) {
 	for _, c := range root.Commands() {
 		names = append(names, c.Name())
 	}
-	for _, want := range []string{"config", "db", "fetch", "migrate", "version"} {
+	for _, want := range []string{"config", "fetch", "migrate", "version", "wsserve"} {
 		if !slices.Contains(names, want) {
 			t.Errorf("job-search has no %q command; has %v", want, names)
 		}