Replace Pyperclip with Qt's native clipboard API for all GUI clipboard operations.

[Zexyen]

Summary

SteamOS does not include wl-clipboard by default. Pyperclip relies on external utilities such as wl-copy and wl-paste under Wayland, which causes clipboard operations to fail on a default SteamOS installation. Since the application already uses PySide6, Qt can provide native clipboard integration across Wayland, X11, and Windows without requiring a separate clipboard package or command-line utility.

Changes

• Added shared Qt clipboard helpers for copying and retrieving text.
• Migrated seed string copy and paste operations to the Qt clipboard.
• Migrated progression point CSV copy and paste operations to the Qt clipboard.
• Removed the Pyperclip dependency.
• Updated the Linux documentation to clarify that external clipboard utilities are not required.
• Added focused tests for Qt clipboard text round-tripping and removal of Pyperclip from migrated files.

Impacts

• SteamOS & other Distros using Wayland: No longer requires wl-clipboard.
• X11 Linux Distributions: No longer requires xclip or xsel.
• Windows: Qt uses the native Windows clipboard API.

This is purely a backend change to how copying to clipboard is done, none of the formatting & other operations are affected.

Tests before Merge

• Confirm all Copy operations works
• Confirm Copying works on Linux in general
• Confirm Copying works on SteamOS (In Progress)
• Confirm Copying works on Windows

[zaktherobot]

Apologies, I have already made the changes for this locally, and forgot to push them up to mainline. I think the only thing that needs to be kept from this PR is the documentation changes.

[Zexyen]

Apologies, I have already made the changes for this locally, and forgot to push them up to mainline. I think the only thing that needs to be kept from this PR is the documentation changes.

Seems we both had the same thought yesterday! I've gone ahead & just set the Documentation Changes in the PR.