fix(shell-execute): optimize working_directory parameter and tool usage hints

[chcodex]

AgentScope-Java Version

Based on upstream/main

Description

Three optimizations for ShellExecuteTool:

1. refactor(tool): Mark working_directory parameter as non-required (required = false)
2. fix(agent): Improve workingDirectory parameter description
3. docs(shell-execute): Add prompt suggesting llm prefer special tools (read_file, write_file, etc.) over shell commands when applicable

How to Test

• Verify working_directory parameter is non-required
• Verify parameter descriptions are clear
• Verify shell tool prompt message is correct

Checklist

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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