Yield initial node during Graph (and therefore Agent) iteration

[dmontagu]

Changes the __aiter__ API for graphs (and consequently agents) to start by yielding the initial input node as the first output of the iterator, rather than skipping that node and only yielding the outputs of calling next (as it currently does).

Closes #1347

[hyperlint-ai]

PR Change Summary

Yield initial node during graph iteration to enhance user interaction with the graph structure.

• Added UserPromptNode to the graph iteration process
• Updated output messages to include user prompts
• Modified documentation to reflect changes in node behavior

Modified Files

• docs/agents.md
• docs/graph.md

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