Update vent control DBC

[wpmed92]

Key corrections vs. the old DBC:

• Byte 0 is a multiplexer (UI_ventPanelControlRequestIndex), not LeftPositionX. Index=0
  carries positions; Index=1 carries modes. (The old PositionX@byte0 was always 0 and never
  moved.)
• Byte layout was wrong. Confirmed by isolated single-axis drags:

• All positions are 8-bit, scale 0.5 (raw 0..200 = 0..100%).
  • Symmetric: each vent is [X, Y, split-X]; "split" adds a 2nd horizontal point sharing one
    Y.