Expand Laravel AI SDK documentation

[emaadali]

Summary

This PR updates the Laravel AI SDK documentation to cover current package usage for recently added and underdocumented APIs.

• Document polymorphic conversation participants, including forParticipant, continueLastConversation, and participant relationships. Related PR: Store conversation participants polymorphically ai#795.
• Document human-in-the-loop tool approvals, including approvable tools, approval decisions, streaming, queueing, broadcasting, and tests. Related PR: Add human-in-the-loop ai#773.
• Document file and multimodal embeddings, including audio, document, image, and video inputs. Related PR: Support multimodal for Gemini and VoyageAI ai#798.
• Document tool choice configuration and runtime toolChoice resolution. Related PR: Add tool choice support for Gemini, OpenAI, and Anthropic ai#780.
• Document summarization helpers via Str::summarize and Stringable::summarize. Related PR: Add summarize macro for text summarization ai#800.
• Document Bedrock configuration, AssumeRole credentials, and S3 document references. Related PRs: Bedrock: support cross-account AssumeRole credential provider ai#566, Bedrock support for remote s3 document  ai#476.
• Document provider options for pending requests, provider tools, and file uploads. Related PRs: Standardize withProviderOptions across the provider option API ai#753, Add withProviderOptions() to storable files ai#717.
• Document web search citations and streaming citation events. Related PR: Add web search and citation support to OpenRouterProvider ai#738.
• Document per-request embedding cache disabling and update provider support coverage. Related PRs: Allow disabling the embeddings cache per request ai#706, OpenRouter TTS and STT support ai#559.

[pushpak1300]

Duplicate of #11295

[GertjanRoke]

@pushpak1300 I noticed that the description of this PR listed some more topics that were not updated inside #11295. For me personally the new Human-in-the-loop is a super helpful feature, but now hard to share internally with other developers.

*Edit: I also saw this PR #11074, so maybe this will tackle it already?