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_ratelimits.go

@@ -8,11 +8,14 @@ import (
 // JSCKServerRateLimits is the server rate limits section's configuration key.
 const JSCKServerRateLimits string = "rate_limits"
 
-// JSCServerRateLimits configures the server's rate limiters. IdleTTL is how
-// long a client's limiter is kept after its last request; 0 or less means
-// limiters are never evicted.
+// JSCServerRateLimits configures the server's rate limits. Global limits
+// every request from each client, and API each client's API requests (see
+// JSCRateLimitRule). IdleTTL is how long a client's limiter is kept after its
+// last request; 0 or less means limiters are never evicted.
 type JSCServerRateLimits struct {
-	IdleTTL time.Duration `cfg:"idle_ttl" default:"10m"`
+	Global  JSCRateLimitRule `cfg:"global"`
+	API     JSCRateLimitRule `cfg:"api"`
+	IdleTTL time.Duration    `cfg:"idle_ttl" default:"10m"`
 }
 
 // ---------- Section methods (see Section) ----------