perf(css): fix rendering slowdown on low-power hardware (Pi5)

- Remove backdrop-filter: blur(5px) from .card and .panel — on ARM/Linux
  Chromium this is software-rendered, causing severe CPU overhead at 42+
  instances. The opaque surface gradient makes blur imperceptible anyway.
- Remove inset vignette box-shadow from .panel added in 51c1014
- Rewrite panel-pulse keyframes to animate opacity only (was box-shadow,
  which triggers CPU repaint every frame; opacity is compositor-only)
- Gate body::before and .visuals-container::after scanline pseudo-elements
  under [data-animations="off"] — the toggle was blind to both
- Gate panel-indicator pulse under [data-animations="off"] for consistency

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/css/core/components.css

@@ -140,7 +140,6 @@
     border-radius: var(--radius-lg);
     overflow: hidden;
     box-shadow: var(--shadow-sm), inset 0 1px 0 rgba(255, 255, 255, 0.04);
-    backdrop-filter: blur(5px);
 }
 
 .card-header {
@@ -177,8 +176,7 @@
     border: 1px solid rgba(74, 163, 255, 0.24);
     border-radius: var(--radius-lg);
     overflow: hidden;
-    box-shadow: var(--shadow-sm), inset 0 0 40px rgba(0, 0, 0, 0.25), inset 0 1px 0 rgba(255, 255, 255, 0.04);
-    backdrop-filter: blur(5px);
+    box-shadow: var(--shadow-sm), inset 0 1px 0 rgba(255, 255, 255, 0.04);
 }
 
 @supports (clip-path: polygon(0 0)) {
@@ -234,14 +232,8 @@
 }
 
 @keyframes panel-pulse {
-    0%, 100% {
-        box-shadow: 0 0 4px var(--status-online), 0 0 8px rgba(56, 193, 128, 0.4);
-        opacity: 1;
-    }
-    50% {
-        box-shadow: 0 0 8px var(--status-online), 0 0 16px rgba(56, 193, 128, 0.6);
-        opacity: 0.85;
-    }
+    0%, 100% { opacity: 1; }
+    50% { opacity: 0.7; }
 }
 
 .panel-indicator.active {
@@ -256,6 +248,10 @@
     }
 }
 
+[data-animations="off"] .panel-indicator.active {
+    animation: none;
+}
+
 .panel-content {
     padding: var(--space-3);
 }