Add config option to set default :comments visibility (outdated/resolved threads)

[eranelbaz]

Problem

Outdated and resolved GitHub review threads are hidden by default (PrCommentsVisibility::Unresolved). Running :comments all shows them, but visibility resets to unresolved for each new session - no way to persist a preferred default.

Request

Add a config key, e.g. pr_comments_visibility, to set default value at startup:

   pr_comments_visibility = "all"  # "unresolved" (default) | "all" | "hide"

Would let users who always want to see outdated/resolved threads skip running :comments all every session.

I can submit pull request to resolve this issue