Fix welcome dashboard jitter and refine Morse mode UI

Fix "What's New" section shifting up/down on smaller screens (#157) by
isolating the logo pulse animation to its own compositing layer, stabilizing
the scrollbar gutter, and pinning the welcome container dimensions.

Morse mode improvements: relocate scope and decoded output panels to the
main content area, use shared SDR device controls, and reduce panel heights
for better layout.

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

static/css/index.css

@@ -206,6 +206,8 @@ body {
     max-width: 900px;
     z-index: 1;
     animation: welcomeFadeIn 0.8s ease-out;
+    max-height: calc(100vh - 40px);
+    overflow: hidden;
 }
 
 @keyframes welcomeFadeIn {
@@ -232,6 +234,7 @@ body {
 
 .welcome-logo {
     animation: logoPulse 3s ease-in-out infinite;
+    will-change: filter;
 }
 
 @keyframes logoPulse {
@@ -332,6 +335,7 @@ body {
     padding: 20px;
     max-height: calc(100vh - 300px);
     overflow-y: auto;
+    scrollbar-gutter: stable;
 }
 
 .changelog-release {

static/css/modes/morse.css

@@ -11,7 +11,7 @@
 
 .morse-scope-container canvas {
     width: 100%;
-    height: 120px;
+    height: 80px;
     display: block;
     border-radius: 4px;
 }
@@ -21,8 +21,8 @@
     background: var(--bg-primary);
     border: 1px solid var(--border-color);
     border-radius: 6px;
-    padding: 16px;
-    min-height: 200px;
+    padding: 12px;
+    min-height: 120px;
     max-height: 400px;
     overflow-y: auto;
     font-family: var(--font-mono);
@@ -30,7 +30,6 @@
     line-height: 1.6;
     color: var(--text-primary);
     word-wrap: break-word;
-    flex: 1;
 }
 
 .morse-decoded-panel:empty::before {
@@ -112,14 +111,6 @@
     gap: 4px;
 }
 
-/* Visuals container layout */
-#morseVisuals {
-    flex-direction: column;
-    gap: 12px;
-    padding: 16px;
-    height: 100%;
-}
-
 /* Word space styling */
 .morse-word-space {
     display: inline;