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/SummaryCurve.svelte

@@ -637,6 +637,20 @@
   @media (max-width: 900px) {
     .signal-panel {
       inline-size: 100%;
+      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);
+    }
+
+    .summary-line {
+      filter: none;
+    }
+
+    .summary-dot {
+      filter: none;
+    }
+
+    .chart-stage {
+      background: linear-gradient(180deg, rgb(var(--hud-surface-alt-rgb) / 0.78), rgb(var(--hud-surface-deep-rgb) / 0.88));
     }
   }
 </style>