Story 4.2: Implement full AV replacement with WebRTC stream access

- Update FoundryAdapter to properly detect and expose WebRTC stream access
- Modify ScryingPoolStrip to create video elements with WebRTC streams
- Add video container to roster-strip.hbs template with conditional rendering
- Add CSS to hide Foundry's AV dock (#av and .camera-view)
- Add CSS styling for video containers and elements
- Fix unused variable in FoundryAdapter.buildWebRTCSurface
- Add comprehensive test script for stream access implementation

Architecture: Full replacement mode where module hides Foundry's AV dock
and creates its own video elements using game.webrtc.client.getMediaStreamForUser()

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

styles/components/_roster-strip.less

@@ -93,6 +93,19 @@
   }
 }
 
+// Video container for WebRTC stream (full AV replacement mode)
+.sp-participant-video {
+  position: absolute;
+  inset: 0;
+  width: 100%;
+  height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  overflow: hidden;
+  z-index: 1;
+}
+
 .sp-avatar__img {
   width: 32px;
   height: 32px;
@@ -101,6 +114,24 @@
   flex-shrink: 0;
 }
 
+// Video element styling
+.sp-participant-video__element {
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+  border-radius: 50%;
+  background: hsl(220, 15%, 18%);
+  
+  .is-expanded & {
+    border-radius: 4px;
+  }
+}
+
+// Hide avatar image when video stream is active (has video element)
+.sp-participant-video:not(:empty) ~ .sp-avatar__img {
+  display: none;
+}
+
 .sp-avatar__corner-badge {
   position: absolute;
   bottom: 2px;
@@ -229,7 +260,7 @@
   z-index: 10;
 
   &::before {
-    content: '\f023'; // fa-lock
+    content: '\f023'; //fa-lock
     font-family: 'Font Awesome 6 Free';
     font-weight: 900;
     font-size: 1.2rem;