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

go.mod

@@ -3,14 +3,20 @@ module git.avsdev.uk/Go/job-search
 go 1.26.8
 
 require (
+	github.com/coder/websocket v1.8.15
+	github.com/dustin/go-humanize v1.0.1
+	github.com/go-chi/chi/v5 v5.4.0
 	github.com/jmoiron/sqlx v1.4.0
 	github.com/joho/godotenv v1.5.1
+	github.com/klauspost/compress v1.20.3
 	github.com/lmittmann/tint v1.2.0
 	github.com/mattn/go-sqlite3 v1.14.52
+	github.com/pires/go-proxyproto v0.15.0
 	github.com/pressly/goose/v3 v3.28.0
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
 	go.yaml.in/yaml/v3 v3.0.5
+	golang.org/x/time v0.16.0
 	resty.dev/v3 v3.0.0-rc.4
 )