Fix MOK Fitness S10 Ultra resistance control (use 0xFFF2 instead of FTMS control point)

[cagnulein]

Summary

• Fixes MOK Fitness S10 Ultra resistance/power issue #4844: auto-resistance still didn't work on the MOK Fitness S10 Ultra after the earlier power-table fix (Compute power from resistance for MOK Fitness S10 Ultra bike #4845), because the bike NAKs FTMS_SET_TARGET_RESISTANCE_LEVEL sent over the standard FTMS control point (0x2AD9).
• Per the reporter's investigation (BLE packet capture of the official MOK Fitness app + confirmation via NRF Connect, see comment), the bike expects resistance changes as a single raw write to a proprietary characteristic (0xFFF2) with the format AF 05 04 <level> AA, no handshake required.
• ftmsbike::forceResistance() now detects MOK_FITNESS and writes that raw command directly to 0xFFF2 instead of going through the FTMS control point; the characteristic/service are discovered and cached during stateChanged() alongside the existing FTMS/Zwift Play discovery.

Test plan

• Reporter to confirm auto-resistance now follows target resistance (e.g. incline changes in MyWhoosh) on the MOK Fitness S10 Ultra
• No local build environment available in this session (Qt not installed); changes reviewed by hand against the existing forceResistance/service-discovery patterns used for similar non-FTMS-control-point bikes (e.g. SL010, SPORT01).

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