Use outer chamber radius for i-support actuation area #98

Context

In ISupportPcsSystem.actuation_matrix, the pressure area of one pneumatic chamber is currently computed from the inner chamber radius:

A_one_chamber = jnp.pi * self.r_chamber_in[i] ** 2

Reference: https://github.com/tud-phi/soromox/blob/am_isupport/src/soromox/systems/pcs/isupport.py#L366

Requested change

Switch this calculation to use the outside chamber radius instead of the inside chamber radius, i.e. use self.r_chamber_out[i] for the chamber pressure area.

Acceptance criteria

• actuation_matrix uses the outside chamber radius for A_one_chamber.
• Any affected tests or fixtures are updated to reflect the corrected actuation area.
• Existing geometry calculations that intentionally depend on the annular cross-section remain unchanged unless explicitly related to this pressure-area correction.