fix(playground): improve OSC UI discoverability and mobile layout

- OSC pill: add status dot indicator (gray=off, green=connected,
  pulsing yellow=connecting), use flexbox for reliable alignment
- OSC pill: add hover state for better affordance
- Synth panel: add separator line above OSC row so it doesn't
  blend into the arpeggiator controls
- Bottom sheet: increase expanded height from 55vh to 60vh so
  OSC row isn't cut off on mobile
- Help modal: update step 3 to mention the OSC pill in the
  bottom bar as the primary connection method

playground/a-immersive.html

@@ -190,7 +190,7 @@
         <div class="synth-row" id="midi-status-row" style="display:none">
           <span class="synth-status" id="midi-status"></span>
         </div>
-        <div class="synth-row" id="osc-row">
+        <div class="synth-row osc-row-panel" id="osc-row">
           <label>OSC Output</label>
           <button class="action-btn" id="osc-toggle">Connect</button>
           <span class="synth-status" id="osc-status">Off</span>
@@ -325,7 +325,7 @@
           <pre class="help-code" id="osc-run-instructions">./nisps-osc-bridge</pre>
 
           <p><strong>3. Connect</strong></p>
-          <p>In the synth panel below, click <strong>Connect</strong> next to "OSC Output". The status will show the target address once connected.</p>
+          <p>Click the <strong>OSC</strong> button in the bottom bar (visible in all modes). The dot turns green when connected. You can also find a Connect button in the synth panel when expanded.</p>
         </div>
 
         <p style="margin-top:10px"><strong>Configuration</strong></p>

playground/css/a-immersive.css

@@ -676,28 +676,68 @@ html, body {
 }
 
 .osc-pill {
-  padding: 4px 12px;
+  padding: 4px 10px;
   border-radius: 6px;
-  border: 1px solid rgba(255, 255, 255, 0.08);
+  border: 1px solid rgba(255, 255, 255, 0.12);
-  background: rgba(255, 255, 255, 0.04);
+  background: rgba(255, 255, 255, 0.05);
   color: var(--text-dim);
-  font-size: 12px;
+  font-size: 11px;
+  font-weight: 500;
+  letter-spacing: 0.5px;
   cursor: pointer;
   transition: all 0.15s;
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+}
+
+/* Dot indicator before text */
+.osc-pill::before {
+  content: '';
+  flex-shrink: 0;
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  background: rgba(255, 255, 255, 0.2);
+  transition: all 0.15s;
+}
+
+.osc-pill:hover {
+  border-color: rgba(255, 255, 255, 0.25);
+  color: var(--text);
+}
+
+.osc-pill:hover::before {
+  background: rgba(255, 255, 255, 0.4);
 }
 
 .osc-pill.connected {
-  background: rgba(0, 200, 120, 0.15);
+  background: rgba(0, 200, 120, 0.12);
-  border-color: rgba(0, 200, 120, 0.4);
+  border-color: rgba(0, 200, 120, 0.35);
   color: #00c878;
 }
 
+.osc-pill.connected::before {
+  background: #00c878;
+  box-shadow: 0 0 4px rgba(0, 200, 120, 0.5);
+}
+
 .osc-pill.connecting {
-  background: rgba(255, 200, 0, 0.1);
+  background: rgba(255, 200, 0, 0.08);
-  border-color: rgba(255, 200, 0, 0.3);
+  border-color: rgba(255, 200, 0, 0.25);
   color: #ffc800;
 }
 
+.osc-pill.connecting::before {
+  background: #ffc800;
+  animation: osc-pulse 1s ease-in-out infinite;
+}
+
+@keyframes osc-pulse {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.3; }
+}
+
 .chevron-btn {
   width: 32px;
   height: 32px;
@@ -741,7 +781,7 @@ html, body {
 }
 
 .bottom-sheet.expanded {
-  height: 55vh;
+  height: 60vh;
   overflow-y: auto;
   -webkit-overflow-scrolling: touch;
 }
@@ -920,6 +960,13 @@ html, body {
   font-size: 12px;
 }
 
+/* OSC row in synth panel — visual separator from arp controls above */
+.osc-row-panel {
+  margin-top: 6px;
+  padding-top: 10px;
+  border-top: 1px solid rgba(255, 255, 255, 0.06);
+}
+
 .synth-status {
   font-size: 11px;
   color: var(--text-dim);