Added the HTTP server and serve command, with proxy, CSRF, TLS and security header config; wsserve is now ws serve, alongside a new ws dial

The serve command runs internal/server: the API under /api (health, and
the CSRF token endpoint) and the WebSocket hub under /ws, over HTTP or TLS,
with an optional HTTP to HTTPS redirect, the PROXY protocol from trusted
sources and a graceful shutdown that closes WebSockets first. Its middleware
covers the client IP behind trusted proxies, request IDs, request logging,
panic recovery, global and API rate limits, Host and body size checks,
security response headers, compression, CSRF protection (cross-origin
checks and signed double-submit tokens) and JSON-only API bodies. Middleware
that logs takes a WithLogger option.

New server config sections: proxy, csrf, tls, headers and frontend (not
used yet), plus max_header_bytes, max_body_bytes, global and API rate limits
and HTTP read, write and idle timeouts. Every setting documents what 0 or
empty means, and internal/config/README.md is reorganised by section.
server.timeouts.read_header must be greater than 0, and a header or idle
timeout of 0 means no limit rather than the read timeout.

WebSocket upgrades are protected by the Origin check: the server's own
origin, or one of csrf.cross_origin_protection.trusted_origins, which the
hub now takes with WithTrustedOrigins.

wsserve becomes "ws serve". "ws dial" opens a WebSocket on /ws to test it:
--ping sends a ping and waits for the pong, --message sends messages and
prints the replies, --origin tests the Origin check, and with neither
--ping nor --message each line of stdin is sent until Ctrl+C.

internal/config/conf_server.go

@@ -1,7 +1,10 @@
 package config
 
 import (
+	"errors"
 	"reflect"
+
+	"git.avsdev.uk/Go/job-search/internal/util"
 )
 
 // JSCKServer is the server section's configuration key.
@@ -9,13 +12,22 @@ const JSCKServer string = "server"
 
 // JSCServer configures the outward server. Host is the address to listen
 // on (empty means every interface) and Port the port (0 means any free
-// port).
+// port). MaxHeaderBytes is the largest request header block; 0 means the
+// default (8KB), and -1 (no limit) is rejected (see validate). MaxBodyBytes is
+// the largest request body; 0 means the default (1MB) and -1 no limit.
 type JSCServer struct {
-	Host       string              `cfg:"host"        default:"127.0.0.1"`
-	Port       int                 `cfg:"port"        default:"9393"`
-	Timeouts   JSCServerTimeouts   `cfg:"timeouts"`
-	RateLimits JSCServerRateLimits `cfg:"rate_limits"`
-	WebSocket  JSCServerWebSocket  `cfg:"websocket"`
+	Host           string              `cfg:"host"             default:"127.0.0.1"`
+	Port           int                 `cfg:"port"             default:"9393"`
+	MaxHeaderBytes util.ByteSize       `cfg:"max_header_bytes" default:"8KB"`
+	MaxBodyBytes   util.ByteSize       `cfg:"max_body_bytes"   default:"1MB"`
+	Timeouts       JSCServerTimeouts   `cfg:"timeouts"`
+	RateLimits     JSCServerRateLimits `cfg:"rate_limits"`
+	Proxy          JSCServerProxy      `cfg:"proxy"`
+	CSRF           JSCServerCSRF       `cfg:"csrf"`
+	TLS            JSCServerTLS        `cfg:"tls"`
+	Headers        JSCServerHeaders    `cfg:"headers"`
+	Frontend       JSCServerFrontend   `cfg:"frontend"`
+	WebSocket      JSCServerWebSocket  `cfg:"websocket"`
 }
 
 // ---------- Section methods (see Section) ----------
@@ -42,3 +54,18 @@ func (c JSCServer) ValueOf(key string) (any, error) {
 func (c *JSCServer) SetValue(key string, value any) error {
 	return setValue(c, key, value)
 }
+
+// ---------- Section specific methods ----------
+
+// validate checks values before they are stored (see validator).
+// max_header_bytes can't be -1 (no limit): the HTTP server always limits the
+// header block, so -1 would quietly mean its own default instead.
+func (c *JSCServer) validate(key string, value any) error {
+	if key == "max_header_bytes" &&
+		value.(util.ByteSize) == util.ByteSizeNoLimit {
+		return errors.New(
+			"config: max_header_bytes can't be -1 (no limit): set an explicit size, or 0 for the default",
+		)
+	}
+	return nil
+}