docs/proxmox.md: moving an install in, upgrading, HAProxy, as tippr's

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proxmox-docs into main

Set out as tippr's PROXMOX.md: before you start, creating the container step by step, behind HAProxy on OPNsense or pfSense (both CARP nodes and the VIP as trusted proxies), media from a share mounted on the node, the GPU, changing settings, and notes. New:

  • Moving an existing install (Windows or Ubuntu) into the container: its data folder (database, sign-in keys, pictures) packed and pushed in, and the library paths changed in the database, as editing them in Admin would start each library afresh and lose its watch history.
  • Upgrading: a snapshot first, the release's .deb installed with apt in a login shell, checking it, and rolling back.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com

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