feat: add traditional IRC wire protocol listener on configurable port

Add a backward-compatible IRC protocol listener (RFC 1459/2812) that
allows standard IRC clients (irssi, weechat, hexchat, etc.) to connect
directly via TCP.

Key features:
- TCP listener on configurable port (IRC_LISTEN_ADDR env var, e.g. :6667)
- Full IRC wire protocol parsing and formatting
- Connection registration (NICK + USER + optional PASS)
- Channel operations: JOIN, PART, MODE, TOPIC, NAMES, LIST, KICK, INVITE
- Messaging: PRIVMSG, NOTICE (channel and direct)
- Info commands: WHO, WHOIS, LUSERS, MOTD, AWAY
- Operator support: OPER (with configured credentials)
- PING/PONG keepalive
- CAP negotiation (for modern client compatibility)
- Full bridge to HTTP/JSON API (shared DB, broker, sessions)
- Real-time message relay via broker notifications
- Comprehensive test suite (parser + integration tests)

The IRC listener is an optional component — disabled when IRC_LISTEN_ADDR
is empty (the default). The Broker is now an Fx-provided dependency shared
between HTTP handlers and the IRC server.

closes #89

internal/handlers/api_test.go

@@ -18,6 +18,7 @@ import (
 	"testing"
 	"time"
 
+	"git.eeqj.de/sneak/neoirc/internal/broker"
 	"git.eeqj.de/sneak/neoirc/internal/config"
 	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/globals"
@@ -213,6 +214,7 @@ func newTestHandlers(
 		Database:    database,
 		Healthcheck: hcheck,
 		Stats:       tracker,
+		Broker:      broker.New(),
 	})
 	if err != nil {
 		return nil, fmt.Errorf("test handlers: %w", err)