fix: stop gyro drift via Eden-matched axis defaults + continuous bias calibration

[NightHammer1000]

Summary

Fixes user reports of gyro drifting over time. Two independent causes, both addressed here.

1. Default axis maps did not match Eden/Yuzu's Cemuhook UDP remap. Closes Default axis maps do not match Eden/Yuzu Cemuhook UDP motion interpretation #3. Eden reads incoming DSU as (pitch, roll, -yaw) for gyro and (accel.x, -accel.z, accel.y) for accel. Our defaults were built for SDL's Steam Triton sensor order, so the emulator received gyro on mismatched axes/signs — visible as continued one-axis drift after motion stopped. AxisMap::DEFAULT now matches Eden's gyro expectation, and a new AxisMap::DEFAULT_ACCEL covers the asymmetric accel remap. Config::DEFAULT.accel wires to the new constant.

2. Continuous gyro bias calibration ported from JibbSmart/GamepadMotionHelpers AddSampleStillness in GamepadMotion.hpp v9 (MIT). SDL's Triton driver and evdevhook2 both punt the zero-rate offset to the consumer; the emulator integrates it as orientation drift. New src/gyro_calibration.rs gates stillness on combined gyro + accel deltas across a growing collection window; once steady, the bias is exponential-LERP'd toward the window-mean gyro with confidence-scaled half-time, so the first lock is instant and later updates are slow (thermal drift). Accel is part of the gate so a slow constant rotation can't masquerade as stillness.

   Owned by OpenSlot, applied right after parse_state. dt comes from imu.timestamp_us clamped to 100 ms. Resets on slot reopen and on axis-map config change. Manual recalibration via the existing Recenter viz button (new stats::RECALIBRATE_REQUEST atomic) — set the controller down, click, gyro is zeroed.

⚠️ Note for existing users

Existing configs at %APPDATA%\sc2dsu\config.toml are not auto-migrated. Anyone who launched a previous version has the old (SDL-ordered) defaults saved as their config and will keep drifting in Eden/Yuzu until they either:

• delete %APPDATA%\sc2dsu\config.toml and let the app write the new defaults on next launch, or
• adjust the gyro/accel axis mapping manually in the settings window to match the new defaults (gyro: X, -Z, Y · accel: -X, -Z, Y).

A clean install picks up the correct defaults automatically. Worth calling out in the release notes for 0.1.4.

Test plan

• CI: cargo fmt --check, cargo clippy -- -D warnings, cargo test --locked, cargo build --release --locked all pass on Windows.
• Manual: fresh install on Windows, Proteus Puck plugged in, launch Eden — gyro behaves correctly without per-axis tweaks.
• Manual: leave controller on desk after launch, confirm gyro values converge to ~0 dps within ~2 s (continuous calibration locks).
• Manual: rotate controller, set it down, hit Recenter viz — gyro recalibrates against the new resting orientation.
• Manual: change axis mapping in the UI mid-session — calibration resets, no stale bias bleed-through.
• Manual: existing-user upgrade path — verify drift persists until config is reset (documents the migration caveat).