fix(ui): lower-overhead Reduced effects for constrained GPUs (#1616)

* fix(ui): lower-overhead Reduced effects path for constrained GPUs

Disable backdrop-filter glass and solidify chrome fills when data-effects is reduced (Calm default), with Appearance warning and docs for constrained rendering devices. Related to #1614.

* test(ui): harden Reduced effects glass e2e and docs wording

Parse Color Level 4 slash alpha so opacity asserts are not vacuously true, cover dialog/toast/overlay both ways with stable data-sn hooks, and soften troubleshooting copy that overstated the unmeasured diagnosis.

* docs(ui): lead constrained-GPU guidance with Reduced Motion

Rename the troubleshooting section to neutral GPU framing, point Appearance and docs at Reduced Motion first, and show the callout whenever Motion is off so Calm or Reduced effects alone do not hide the validated workaround.

docs/reference/settings.mdx

@@ -118,7 +118,8 @@ Control how Sencho looks and how dense the workspace feels. Each browser remembe
 | Control | What it does |
 |---------|--------------|
 | **Chart palette** | Colors the Security page charts: **Muted**, **Heat** (one warm ramp), or **Signature** (saturated). |
-| **Reduced effects** | Flattens card bevels, the accent glow, and chart gradients. |
+| **Reduced motion** | Minimizes interface animations and transitions. First control to try for high idle GPU use on constrained graphics. Toasts are unaffected. |
+| **Reduced effects** | Flattens card bevels, the accent glow, and chart gradients, and turns off glass blur with solid chrome fills. Optional secondary material simplification; not a substitute for Reduced motion on the reported idle-GPU symptom. |
 | **Ambient glow** | Intensity of the accent-tinted page glow. |
 
 ### Theme and typography