perf: optimize mobile line chart performance and remove window controls

- Remove drop-shadow filters on SVG paths on mobile (SignalChart, SummaryCurve)
- Hide scan-haze overlay (mix-blend-mode: screen) on mobile
- Remove feTurbulence noise filter on mobile (biggest perf win)
- Simplify backgrounds and box-shadows on mobile
- Remove blur transition on inactive panels
- Hide window control buttons (minimize/maximize/close) on mobile
- Configure Android release build to sign with debug keystore
- Update README with changelog and Android build instructions

src/lib/components/SignalChart.svelte

@@ -200,7 +200,6 @@
     border-color: transparent;
     opacity: 0;
     transform: translateX(var(--offset-x)) scale(0.98) rotate(-0.6deg);
-    filter: blur(1.3px);
     pointer-events: none;
     transition-delay: 0ms;
   }
@@ -302,6 +301,7 @@
     stroke-linecap: round;
     stroke-linejoin: round;
     filter: drop-shadow(0 0 2px rgb(0 0 0 / 0.42));
+    will-change: d;
   }
 
   .series-line.tone-cyan {
@@ -397,6 +397,10 @@
       aspect-ratio: 1.5 / 1;
       min-block-size: 10.1rem;
     }
+
+    .chart-stage {
+      block-size: clamp(5.7rem, 7.6vw, 6.9rem);
+    }
   }
 
   @media (max-height: 900px) {
@@ -452,6 +456,21 @@
       inline-size: 100%;
       aspect-ratio: 1.7 / 1;
       min-block-size: 0;
+      background: linear-gradient(160deg, rgb(var(--hud-surface-alt-rgb) / 0.86) 0%, rgb(var(--hud-surface-deep-rgb) / 0.9) 100%);
+      box-shadow: inset 0 0 0 1px rgb(var(--hud-border-strong-rgb) / 0.08), 0 0 8px rgb(var(--hud-glow-rgb) / 0.1);
+    }
+
+    .series-line {
+      filter: none;
+    }
+
+    .scan-haze {
+      display: none;
+    }
+
+    .chart-stage {
+      background: linear-gradient(180deg, rgb(var(--hud-surface-alt-rgb) / 0.78), rgb(var(--hud-surface-deep-rgb) / 0.88));
+      box-shadow: none;
     }
   }
 </style>