Fix ComplexConjugateControl reactive-gain sign error (K_r double-negative)

[Copilot]

ComputeCCGains computed K_r = −ω²(I+A) + K_hs, which combined with the control law τ = −K_r·θ yielded τ_react = +(ω²(I+A) − K_hs)·θ — the wrong sign. The reactive torque reinforced the flap's reactance instead of cancelling it, causing ±0.92 rad runaway amplitude and negative mean absorbed power.

Changes

• src/impedance.cpp — ComputeCCGains (one-line fix + explanatory comment):

  // Before (wrong — double-negative):
  gains.K_r = -omega0 * omega0 * (I_flap_kgm2 + A55) + K_hs55;
  // After — K_r is the intrinsic pitch reactance; control law applies conjugate sign (−K_r·θ):
  gains.K_r = omega0 * omega0 * (I_flap_kgm2 + A55) - K_hs55;

• src/impedance.h, src/active_pto.h, docs/CONTROLLERS.md — updated K_r formula in all doc comments/gain-derivation blocks to reflect the corrected sign.

ComplexConjugateControl::ComputeForce, all other controllers (passive, opt_passive, exc_ff_pid), PitchImpedanceMagnitude, and the CSV schema are unchanged.