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/HudPanel.svelte

@@ -460,6 +460,12 @@
     color: rgb(var(--hud-orange-rgb) / 0.96);
   }
 
+  @media (max-width: 900px) {
+    .window-controls {
+      display: none;
+    }
+  }
+
   .control-bar {
     display: grid;
     gap: 0.45rem;