Review and update Spanish translation of NTP Pool website

[Copilot]

This PR provides a comprehensive review and update of the Spanish translation for the NTP Pool website, bringing it up to date with the current English source content.

Changes Made

1. Updated i18n/es.po translations

• Added missing zone names: Europa, Oceanía
• Added missing index.html strings: Introducción, Servidores Activos, Enlaces, Términos de servicio, Suscribirse en un lector, Noticias anteriores
• Added missing mailinglists.html strings: Foro del Pool NTP, Sitio de noticias, Desarrollo, forum_description, news_description
• Updated existing translations:
  • "The mailing lists" → "Comunidad" (to match English change)
  • Updated development_list_description to reference development forum instead of mailing lists
• Added new translation: "Can you translate?" → "¿Puedes traducir?"

2. Updated HTML templates

docs/ntppool/es/homepage/intro.html

• Updated hosting provider information from outdated "Packet y NetActuate" to current "Equinix Metal"
• Updated community reference from "listas de correo" to "foro de la comunidad del proyecto"

docs/ntppool/es/use.html

• Modernized Windows configuration instructions to match current GUI approach instead of outdated command-line methods
• Added IPv6 information section explaining 2.pool.ntp.org prefix for IPv6 addresses
• Added critical use warning section for business/life-critical applications with hardware vendor recommendations
• Updated technical accuracy and link references

docs/ntppool/es/join.html

• Fixed character encoding issues with Spanish characters
• Updated terminology from "grupo NTP" to "Pool NTP" for consistency

docs/ntppool/es/join/configuration.html

• Fixed typos: "sevidores" → "servidores"
• Translated remaining English sections to Spanish
• Added missing IETF BCP reference section
• Added missing PTR DNS queries warning section
• Updated terminology for consistency with "pool" vs "grupo"

docs/ntppool/es/tpl/server/graph_explanation.html

• Updated content structure to match current English version
• Fixed RFC link to current version (tools.ietf.org instead of eecis.udel.edu)
• Improved technical accuracy of monitoring system explanations

Translation Quality

All translations maintain proper Spanish language conventions and technical terminology. The content is now consistent with the current English source while preserving the existing translation quality and style.

Fixes #260.

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