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/customer-segmentation-server/src/mcp-app.css

@@ -37,7 +37,7 @@ html, body {
 }
 
 .main {
-  width: 600px;
+  width: 100%;
   height: 600px;
   margin: 0 auto;
   padding: 12px;