Add confirmed account deletion to the admin account list

[Gregor-von-Vitek]

Add confirmed account deletion to the admin account list

Summary

• Add a Delete action beside Edit on /accounts.
• Require confirmation that names the account and explains that its characters, items, and related data will be removed.
• Delete through a fresh persistence context and refresh the account list after success. The account aggregate deletion and database cascades remove dependent data, including the vault.
• Update the admin panel documentation.

Verification

• AdminPanel build on a clean branch from upstream/master (-p:ci=true)
• Web.Tests on the clean branch (-p:ci=true, 95 passed)
• Manually verified the action in a local admin panel

The server should be stopped or the account disconnected before deleting an account that is online.