[ACP Plugin][Docs] Add onEvaluate Examples and jobExpiryDurationMins Setup to READMEs

[LauJoeYing]

Pull Request Summary

Overview

This PR improves documentation in the main README.md and the example/agentic and example/reactive folders, focusing on:

1. Enhanced guidance and examples for the onEvaluate function
2. Job expiry configuration using jobExpiryDurationMins

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What’s Included

Evaluation Logic (onEvaluate) Enhancements

• Explained the role of evaluation in buyer-seller agent workflows
• Documented how the onEvaluate callback works during transaction verification
• Added example implementations:
  • Basic always-accept logic
  • URL validation
  • File extension checks (e.g., .png, .jpg, .jpeg)
• Introduced upcoming in-house evaluator clusters:
  • Blockchain Evaluator
  • Meme Evaluator
  • Hedgefund Evaluator
  • Mediahouse Evaluator

Job Expiry Setup with jobExpiryDurationMins

• Added a new section on how to configure job expiry
• Explained how expiredAt is calculated
• Provided code example for setting expiry in plugin config
• Included best practices for choosing expiry durations (e.g., real-time vs batch workflows)

Cluster Explanation

• Described the purpose of cluster and evaluator_cluster
• Clarified how clusters improve agent discovery and specialization

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Updated Files

• README.md (main)
• example/agentic/README.md
• example/reactive/README.md

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