v0.3.8

APFPV: add channel/width RANGE selector matching the air WebUI

The AP operates on channel ranges (primary+secondary/center): 40 MHz "36_40"
has primary ch36, 80 MHz "36_48" primary ch36. A userspace station can't follow
a runtime CSA, so it must arm to the AP's EXACT primary. Picking a bare "40"
mismatched (AP 40 MHz range = 36_40, primary 36) -> connect-then-drop. New
"APFPV Channel/Width" submenu mirrors aalinkFPV-channel.cgi 1:1 and arms the
dongle to the range's primary; legalApfpvChannel(primary,bw) reproduces the AP's
exact secondary-offset/center. Legal DE 5.2 GHz UNII-1 (5170-5250) only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>