VNC browser resource does not support clipboard sync (unlike RDP)

[marcolino7]

Summary

Browser-based VNC resources do not support clipboard sync between the local machine and the remote session, unlike RDP resources which explicitly support it.

Motivation

Browser-based RDP resources support clipboard copy/paste, as documented. Browser-based VNC resources do not appear to have any equivalent — copying text inside the remote VNC session does not sync with the local clipboard, and there's no clipboard bridge panel in the VNC viewer UI either.
This creates an inconsistent experience between the two protocols offered side by side in Pangolin. For day-to-day use (e.g. pasting commands, URLs, or config snippets into a remote Linux desktop), lack of clipboard support makes browser VNC significantly less practical than the RDP equivalent, and often forces users to switch to RDP (e.g. via xrdp) purely to get clipboard, even when VNC would otherwise be the better fit (simpler setup, lighter weight, non-Windows targets).

Proposed Solution

Add clipboard sync for VNC resources, similar to what's already implemented for RDP. This would likely require:

A VNC clipboard bridge on the client side, supporting the RFB ClientCutText/ServerCutText messages, which most modern VNC servers (e.g. TigerVNC) already implement
On the server side, most VNC servers need something like autocutsel (X11) running to bridge the X11 selection buffer with the RFB clipboard channel — this is already common practice and shouldn't require any Pangolin-side host changes beyond documentation

Alternatives Considered

No response

Additional Context

Tested with a Debian 13 + Xfce + TigerVNC target behind a Newt site connector, Pangolin VNC public resource. autocutsel is running server-side but clipboard doesn't sync through the browser session, suggesting the client-side bridge is missing.