Optional steering smoothing mode (slew-rate limiter on stick_x)

[alondero]

Parent

Follows configurable steering shaping.

What to build

An opt-in slew-rate limiter on the steering axis only (stick_x), applied host-side after the shaping from the previous ticket:

• Configurable attack/release rates (units per frame toward the target), or equivalent time-constant form
• Off by default — default must remain instant, faithful passthrough
• Return-to-center rate separately tunable from steer-into-corner rate (players typically want snappier centering than wind-in)

This directly addresses the ROM's missing rate limit: unlike throttle (which ramps ±10/frame toward its target), the ROM recomputes steer demand instantly every frame, which is the core of the twitchy feel on modern high-resolution sticks.

Acceptance criteria

• Smoothing math unit-tested: step response, release-to-center, direction reversal, off-mode passthrough
• Deterministic given identical input sequences (frame-counted, no wall clock)
• UI toggle + rate settings persisted per-controller profile
• Default off reproduces previous behaviour exactly
• Playtest: with smoothing on, hairpin entry is controllable without losing the ability to flick-steer when set to fast rates

Blocked by

• Configurable steering shaping: sensitivity gain, deadzone, response curve #140 Configurable steering shaping: sensitivity gain, deadzone, response curve