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/features/appearance.mdx

@@ -45,9 +45,13 @@ The **Chart palette** sets the colors used on the Security page charts:
 
 ## Motion & effects
 
-- **Reduced effects** flattens card bevels, the accent glow, and chart gradients for a calmer, flatter surface.
+- **Reduced motion** minimizes interface animations and transitions (dialogs, menus, expand and collapse). Toasts are unaffected. On constrained graphics, this is the first control to try when the active Sencho tab feels heavy on idle.
+- When Reduced motion is off, Appearance shows a short notice about constrained graphics and points you at Reduced motion.
+- **Reduced effects** flattens card bevels, the accent glow, and chart gradients, and uses a simpler rendering path: glass blur is off and chrome fills are solid. Fresh installs get this through the default **Calm** visual style. Treat it as an optional secondary experiment for material cost; it is not a substitute for Reduced motion on the reported idle-GPU symptom. The impact varies by device, browser, and graphics configuration.
 - **Ambient glow** sets the intensity of the soft, accent-tinted glow behind the page. Slide it to zero for a completely flat background. (Reduced effects already dims it.)
 
+If the active Sencho tab feels heavy on constrained graphics, see [High GPU usage on constrained graphics](/operations/troubleshooting#high-gpu-usage-on-constrained-graphics).
+
 ## Theme
 
 The **Mode** control sets the overall surface palette:

docs/operations/troubleshooting.mdx

@@ -9,6 +9,23 @@ description: Solutions to the most common Sencho setup and runtime problems.
 
 If something has broken and you want a quick "what do I do now?" overview rather than a specific symptom, start with the [Recovery guide](/operations/recovery). It walks through getting back to a working state when Sencho, a deploy, sign-in, Docker, or a remote node fails, and links back here for the details.
 
+## High GPU usage on constrained graphics
+
+**Symptom:** With Sencho as the active browser tab, GPU use stays high on idle, and can climb further when an update or deploy dialog is open. Other sites in the same browser stay quieter. On some dual-GPU PCs the issue shows up only when the browser is forced onto integrated graphics.
+
+**What helped on the reported Windows configuration:** Turning on **Reduced motion** dropped idle iGPU use substantially (about 50% to about 7% in that report). **Calm** and **Reduced effects** alone did not. On that machine the issue did not appear when Windows selected the GPU or when Chrome used the discrete GPU.
+
+**What to try:**
+
+1. Open **Settings → Appearance → Motion & effects**.
+2. Turn on **Reduced motion**. That is the first step to try for high idle GPU use on constrained graphics.
+3. Optionally try **Reduced effects** or **Calm** as a secondary experiment (simpler glass and solid chrome). That path is unverified for this symptom.
+4. On dual-GPU Windows PCs, you can also set the browser's GPU preference to let the OS decide, or prefer a discrete GPU, if your OS exposes that control.
+
+**How to help validate a fix on your hardware:** Identify Chrome's GPU process (Shift+Esc), use Task Manager Details at High update speed on that PID's GPU column, leave the Sencho tab in the foreground for about 15 seconds, then record about ten one-second samples and take the median. Repeat for at least three independent runs (close and reopen the tab). Compare idle Home or Settings with Reduced motion off versus on. Separately compare an update or deploy dialog with Raw output hidden and visible. On Linux single-board devices, use one documented GPU or responsiveness counter for the whole matrix, and label CPU-only readings as secondary.
+
+---
+
 ## Containers won't start after deploy
 
 **Symptom:** You click Deploy and containers immediately exit or never appear.

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