Feat/agui strands pattern

[razkenari]

Summary

Adds AG-UI protocol support to FAST with two new agent patterns (agui-strands-agent, agui-langgraph-agent), a shared frontend parser, and restructures the project layout for consistency across all patterns.

Changes

Commit 1: Restructure agent patterns and shared modules

• Rewrite strands-single-agent and langgraph-single-agent with consistent structure — each pattern now has its own tools/ module (gateway, code_interpreter) and imports shared utilities from utils/
• Pin all Python dependency versions with == in requirements.txt
• Fix langgraph parser to use LangChain standard tool_call_chunks for tool input streaming
• Fix all Dockerfile COPY paths to match current directory layout

Commit 2: Add AG-UI agent patterns and frontend support

• agui-strands-agent: Strands agent wrapped with ag-ui-strands (StrandsAgent). Creates agent per-request to ensure correct Memory scoping and fresh MCP connections.
• agui-langgraph-agent: LangGraph agent wrapped with copilotkit (LangGraphAGUIAgent). Uses ActorAwareLangGraphAgent subclass to rebuild the graph per-request for fresh Gateway tokens.
• Frontend AG-UI parser (parsers/agui.ts): Maps AG-UI events (TEXT_MESSAGE_CONTENT, TOOL_CALL_START, etc.) to the shared StreamEvent types. Auto-selected for any pattern with agui- prefix.
• AG-UI payload format: AgentCoreClient.invoke() automatically sends RunAgentInput (threadId, messages, runId) for agui-* patterns.
• Documentation: docs/AGUI_INTEGRATION.md — covers architecture, patterns, frontend integration, deployment, and CopilotKit reference.
• Bump CDK dependencies (@aws-cdk/aws-bedrock-agentcore-alpha, @aws-cdk/aws-bedrock-alpha)
• Add AGUI protocol comments in backend-stack.ts and config.yaml

Key design decisions

• Both AG-UI patterns use BedrockAgentCoreApp as the entrypoint (not standalone FastAPI), so AgentCore Runtime headers (WorkloadAccessToken, Authorization, Session-Id) are available for Gateway auth, Memory, and secure user identity extraction from JWT.
• AG-UI patterns deploy with HTTP protocol — AgentCore Runtime's AGUI protocol flag only changes error formatting (RUN_ERROR events vs HTTP error codes). The agent container handles AG-UI event formatting internally.
• One parser for all AG-UI patterns — both Strands and LangGraph AG-UI wrappers produce standard AG-UI events, so a single parseAguiChunk parser handles both.
• CopilotKit kept separate — CopilotKit is referenced in docs as an optional richer frontend.

Testing

• Deployed and validated all 4 strands-single-agent, langgraph-single-agent, agui-strands-agent, and agui-langgraph-agent patterns end-to-end (CDK deploy → AgentCore Runtime → Amplify frontend)
• Verified: text streaming, tool calls (Gateway + Code Interpreter), Memory persistence, user identity extraction