Add Component Embedding Feature

[sambhavnoobcoder]

Description of Changes
This PR adds the ability to embed individual Preswald components or entire applications in external websites. Users can now:

1. Embed specific components by their ID using iframe tags
2. Specify which component to embed via the component_id parameter
3. View embedded components with proper styling and minimal UI clutter
4. Handle errors gracefully when embedding nonexistent components

The implementation includes server-side changes to filter components by ID, frontend changes to support embed mode, and extensive test coverage to ensure reliability.

Related Issue
Fixes #536

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update
• New example
• Test improvement

Testing
I've created comprehensive tests in tests/embed_test.py that verify:

• Component registration with embed mode
• Handling of nonexistent components
• Broadcasting components to clients
• Client unregistration and connection cleanup

All tests pass successfully. I've also manually tested embedding components in the provided example HTML file.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have run my code against examples and ensured no errors
• Any dependent changes have been merged and published in downstream modules