Add configurable bitrate limit and improve unlock bitrate behavior

[Hans155922]

This PR introduces a configurable maximum bitrate (bitrateMax) and improves the behavior of the "Unlock bitrate limit" feature.


• Introduce a UI dropdown to select maximum bitrate (up to 25 Gbps)
• Update slider range and step size to scale with the selected maximum bitrate
• Hide "Use Default" button when unlock mode is enabled
  
  Previously, the bitrate limit was hardcoded, which restricted users on high-speed networks (e.g., 2.5G/10G LAN).This change allows advanced users to fully utilize their available bandwidth.

[andygrundman]

I'll humor you, what GPUs have you used and what sort of bitrate have you been able to achieve from their video encoders?

[Hans155922]

I'll humor you, what GPUs have you used and what sort of bitrate have you been able to achieve from their video encoders?

Good question. I’m currently using an RTX 5080 for encoding, and a mini PC with a 7840HS for decoding.
I’ve tested bitrates up to around 2000 Mbps, but it had packet loss due to network drops.
Dropping it down to about 800 Mbps made things stable. Still in the process of testing and fine-tuning.