refactor: shared service layer, default IRC port, smaller functions

Wire up service.Service in HTTP handlers and delegate cleanupUser to
svc.BroadcastQuit for consistent quit/part logic across transports.
Default IRC_LISTEN_ADDR to :6667, remove unused import, fix all lint
issues (dogsled, funcorder, wrapcheck, varnamelen, nolintlint).

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

internal/ircserver/server.go

@@ -11,6 +11,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/config"
 	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
+	"git.eeqj.de/sneak/neoirc/internal/service"
 	"go.uber.org/fx"
 )
 
@@ -23,6 +24,7 @@ type Params struct {
 	Config   *config.Config
 	Database *db.Database
 	Broker   *broker.Broker
+	Service  *service.Service
 }
 
 // Server is the TCP IRC protocol server.
@@ -31,6 +33,7 @@ type Server struct {
 	cfg      *config.Config
 	database *db.Database
 	brk      *broker.Broker
+	svc      *service.Service
 	listener net.Listener
 	mu       sync.Mutex
 	conns    map[*Conn]struct{}
@@ -49,6 +52,7 @@ func New(
 		cfg:      params.Config,
 		database: params.Database,
 		brk:      params.Broker,
+		svc:      params.Service,
 		conns:    make(map[*Conn]struct{}),
 		listener: nil,
 		cancel:   nil,
@@ -133,7 +137,7 @@ func (s *Server) acceptLoop(ctx context.Context) {
 
 		client := newConn(
 			ctx, tcpConn, s.log,
-			s.database, s.brk, s.cfg,
+			s.database, s.brk, s.cfg, s.svc,
 		)
 
 		s.mu.Lock()