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

cmd/neoircd/main.go

@@ -2,11 +2,13 @@
 package main
 
 import (
+	"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"
 	"git.eeqj.de/sneak/neoirc/internal/handlers"
 	"git.eeqj.de/sneak/neoirc/internal/healthcheck"
+	"git.eeqj.de/sneak/neoirc/internal/ircserver"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
 	"git.eeqj.de/sneak/neoirc/internal/middleware"
 	"git.eeqj.de/sneak/neoirc/internal/server"
@@ -28,16 +30,22 @@ func main() {
 
 	fx.New(
 		fx.Provide(
+			broker.New,
 			config.New,
 			db.New,
 			globals.New,
 			handlers.New,
+			ircserver.New,
 			logger.New,
 			server.New,
 			middleware.New,
 			healthcheck.New,
 			stats.New,
 		),
-		fx.Invoke(func(*server.Server) {}),
+		fx.Invoke(func(
+			_ *server.Server,
+			_ *ircserver.Server,
+		) {
+		}),
 	).Run()
 }