feat: Add support for AG-UI

[adlio]

Adds an AG-UI "bridge" to enable Strands Agents to be the backend for an agentic frontend like Copilot Kit.

Description

Posting this for draft review and considering... continuing to work on docs and examples for using this.

Documentation PR

TBD

Type of Change

• New features

Testing

Used this version of Strands to build an interactive web-based Tic Tac Toe against Claude via Bedrock.

Checklist

• I have read the CONTRIBUTING document
• I have added tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature
• My changes generate no new warnings
• Any dependent changes have been merged and published

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[ryanycoleman]

Addresses #140

[zastrowm]

Based on the current implementation, this looks like several related features are part of this. Specifically, I think we need we're seeing gaps in:

• Session/agent-state ([FEATURE] Add Database Session Management #33, [FEATURE] Community-driven session management #57) (CC @Unshure)
• Multi-agent integration (can't find any direct issues related, but I know @awsarron will be looking at)
• Built-in tools ([FEATURE] Develop strategy for vending tools tools#31)

[adlio]

Based on the current implementation, this looks like several related features are part of this. Specifically, I think we need we're seeing gaps in:

* Session/agent-state ([[FEATURE] Add Database Session Management #33](https://github.com/strands-agents/sdk-python/issues/33), [[FEATURE] Community-driven session management #57](https://github.com/strands-agents/sdk-python/issues/57)) (CC @Unshure)

* Multi-agent integration (can't find any direct issues related, but I know @awsarron will be looking at)

* Built-in tools ([[FEATURE] Develop strategy for vending tools tools#31](https://github.com/strands-agents/tools/issues/31))

Thanks for the review @zastrowm. Yes! This PR as-is would be valuable but not sufficient. I'm continuing to work on a sample/docs updates, etc. I'll review those other bits to see if the agent state and built-in tools work could align as well.