Fix steering sign conventions, rework friction, and add engine RPM vibration

Fix the reversed wheel centering source and soft lock damping (iRacing's steering telemetry is counterclockwise-positive; conventions now documented in CLAUDE.md), and replace the velocity-based friction model with a lead-compensated stick-point model that cannot self-oscillate on the frame-late telemetry.

Add an engine RPM vibration generator with V8-style voicing (harmonics, per-firing jitter, 8-firing lope) and a roughness knob, gated on the EngineWarnings stalled flag and driven by the car's redline RPM — now captured in recordings (format v5; bundled recordings migrated) and plumbed through the tick context.

Also curve the road texture speed ramp (cube root to 180 MPH), drive the slip texture amplitude from the summed understeer + oversteer effects with a both-disabled notice in the editor, keep gear change vibration from replaying stale shifts on re-enable, fix a shutdown race in the constant force effect update, and adopt the tuned module defaults from the maintainer's test graph.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: mherbold

CLAUDE.md

@@ -126,6 +126,12 @@ The post-build step copies several asset folders (sounds, recordings, calibratio
 
 ## Architecture & Key Patterns
 
+### Steering / FFB sign conventions (get these right!)
+- **iRacing steering telemetry is counterclockwise-positive:** `SteeringWheelAngle` (and `SteeringWheelVelocity`) are **positive when the wheel is turned LEFT**, negative when turned right. The derived `FFBTickContext.WheelPosition` / `WheelVelocity` (angle/velocity normalized to the car's half-lock) inherit this same convention.
+- **FFB graph output torque is also counterclockwise-positive:** a positive module output pushes the wheel LEFT.
+- **Consequence:** any resisting/restoring force built from these values (friction, damping, centering, soft lock) must **negate** the telemetry-derived term — e.g. the wheel-centering source returns `-position`, and the friction/velocity sources return `-velocity`. Getting this wrong flips a stable centering spring into a runaway force toward the locks (this bug actually shipped once).
+- **The old DirectInput axis convention was the opposite** (positive = turned right), so any formula ported from pre-graph fixed-function code that used `DirectInput.ForceFeedbackWheelPosition/Velocity` needs its sign flipped when fed the sim-telemetry-derived values.
+
 ### Global Singleton (`App`)
 `App` (in `App.xaml.cs`) is the central singleton accessed via `App.Instance!`. It owns and initializes every component. All components call `App.Instance!` to access sibling services. This is the primary way components communicate.