Fix widget layout to use full available width

- Change marketing widget containers from fixed 600px to width: 100%
- Update basic-host iframe to use flex: 1 for proper expansion
- Widgets now fill their parent container instead of fixed size

Files changed:
- examples/budget-allocator-server/src/mcp-app.css
- examples/customer-segmentation-server/src/mcp-app.css
- examples/scenario-modeler-server/src/mcp-app.css
- examples/system-monitor-server/src/mcp-app.css
- examples/basic-host/src/index.module.css

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

examples/basic-host/src/index.module.css

@@ -113,9 +113,8 @@
   min-height: 200px;
 
   iframe {
-    flex-shrink: 0;
-    height: 100%;
-    max-width: 100%;
+    flex: 1 0 auto;
+    height: 600px;
     box-sizing: border-box;
     border: 3px dashed #888;
     border-radius: 4px;