Add VGOSWEC capture-efficiency sweep/plot workflow (VGM-0/10/20/45/90, T=2–7 s)

[Copilot]

This PR adds a dedicated capture-efficiency analysis path for tuned exc_ff_pid across all five VGOSWEC flap variants on a shared T=2.0..7.0 s grid, with η(T)=P_capture(T)/P_opt(T) and explicit reactive-limited masking where P_opt is undefined.

• New analysis driver (scripts/capture_efficiency_sweep.py)

  • Runs per-flap headless sweeps using merged tuned configs (vgoswec_{0,10,20,45,90}_exc_ff_pid.yaml), no gain retuning.
  • Computes P_capture(T) as steady-state mean absorbed power from the second half of each run.
  • Writes per-flap CSVs: analysis/capture_efficiency_VGM{0,10,20,45,90}.csv with:
    T_s, omega_rads, P_capture_W, P_opt_W, B55_Nmsrad, F_exc_Nm, eta, masked.
  • Generates per-flap figures and cross-flap summary:
    analysis/figures/capture_efficiency_VGM{...}.png, capture_efficiency_summary.png.
  • Supports --plot-only to regenerate figures from committed CSVs.

• Hydrodynamic P_opt implementation

  • Uses H5 body/flap pitch terms directly:
    • body1/hydro_coeffs/radiation_damping/components/5_5
    • body1/hydro_coeffs/excitation/mag at DOF5 (index 4), direction 0
  • Applies WEC-Sim/BEMIO de-normalization:
    • B55 = B55_norm * rho * omega
    • |F_exc| = mag * rho * g * A, with A = 0.014 m (H=0.028 m)
  • Evaluates P_opt = |F_exc|^2 / (8*B55) only where defined.

• Reactive-limited masking and presentation

  • Masks periods with B55 <= 1e-4 (includes non-positive B55), sets P_opt/eta undefined there.
  • Shaded/hatched masked regions in plots.
  • Explicit VGM-0 annotation near resonance for reactive-limited undefined efficiency (B55 → 0).

• Documentation updates

  • analysis/README.md: method, formulae, CSV schema, masking rationale, regeneration commands, VGM-0 caveat.
  • docs/CONTROLLERS.md: capture-efficiency sweep section aligned with H5 source/de-normalization/masking conventions.

# Core denominator + mask logic used in the new sweep
B55 = B55_norm * rho * omega
F_exc = exc_mag * rho * g * A  # A = H/2 = 0.014 m
masked = B55 <= 1e-4
P_opt = np.where(~masked, (F_exc**2) / (8.0 * B55), np.nan)
eta = np.where(~masked, P_capture / P_opt, np.nan)