feat: add IRC wire protocol listener with shared service layer

Add a traditional IRC wire protocol listener (RFC 1459/2812) on
configurable port (default :6667), sharing business logic with
the HTTP API via a new service layer.

- IRC listener: NICK, USER, PASS, JOIN, PART, PRIVMSG, NOTICE,
  TOPIC, MODE, KICK, QUIT, NAMES, LIST, WHOIS, WHO, AWAY, OPER,
  INVITE, LUSERS, MOTD, PING/PONG, CAP
- Service layer: shared logic for both transports including
  channel join (with Tier 2 checks: ban/invite/key/limit),
  message send (with ban + moderation checks), nick change,
  topic, kick, mode, quit broadcast, away, oper, invite
- BroadcastQuit uses FanOut pattern (one insert, N enqueues)
- HTTP handlers delegate to service for all command logic
- Tier 2 mode operations (+b/+i/+s/+k/+l) use service methods

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/neoircd/main.go

@@ -2,14 +2,17 @@
 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"
+	"git.eeqj.de/sneak/neoirc/internal/service"
 	"git.eeqj.de/sneak/neoirc/internal/stats"
 	"go.uber.org/fx"
 )
@@ -28,16 +31,23 @@ 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,
+			service.New,
 			stats.New,
 		),
-		fx.Invoke(func(*server.Server) {}),
+		fx.Invoke(func(
+			_ *server.Server,
+			_ *ircserver.Server,
+		) {
+		}),
 	).Run()
 }