Quality floor overrides an explicit --bitrate with no way to go lower #80

_quality_floor_kbits in src/wfd.py enforces a minimum of 8000 kbit for 1080p30, so --bitrate 4M gets silently raised to 8M:

[FluxCast WFD Media] Raising bitrate for desktop clarity: 4M -> 8M

The floor makes sense as a default for readability, but right now there's no escape hatch. If the Wi-Fi Direct link can't carry 8 Mbps, packets get dropped, the sink can only decode keyframes and keeps asking for IDRs, and the picture ends up updating about once per second. The only workaround is dropping to 720p, which has a lower floor.

Either the floor should not override a bitrate the user explicitly asked for, or there should be a flag to opt out of it.