refactor: standardize logging on zap across all packages

Replace all fmt.Printf/Println and log.Printf/Fatal with structured
zap.Logger calls to eliminate inconsistent logging (anti-pattern #12).

- network/crypt_conn: inject logger via NewCryptConn, replace 6 fmt calls
- signserver/session: use existing s.logger for debug packet dumps
- entranceserver: use s.logger for inbound/outbound debug logging
- api/utils: accept logger param in verifyPath, replace fmt.Println
- api/endpoints: use s.logger for screenshot path diagnostics
- config: replace log.Fatal with error return in getOutboundIP4
- deltacomp: replace log.Printf with zap.L() global logger

server/signserver/sign_server.go

@@ -101,7 +101,7 @@ func (s *Server) handleConnection(conn net.Conn) {
 		logger:    s.logger,
 		server:    s,
 		rawConn:   conn,
-		cryptConn: network.NewCryptConn(conn, s.erupeConfig.RealClientMode),
+		cryptConn: network.NewCryptConn(conn, s.erupeConfig.RealClientMode, s.logger),
 	}
 
 	// Do the session's work.