fix(core): ignore hidden files when loading skill resources

[jujn]

Description

Close #1000

Checklist

Please check the following items before code is ready to be reviewed.

• 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

[Copilot]

Pull request overview

This PR addresses issue #1000 by updating skill resource loading to ignore hidden/dot-prefixed files, preventing unwanted artifacts (e.g., .DS_Store) from being included in AgentSkill resources.

Changes:

• Add filtering in SkillFileSystemHelper.loadResources(...) to skip dot-prefixed and hidden/unreadable files.
• Add a unit test to verify dot-prefixed files are excluded from loaded resources.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
agentscope-core/src/main/java/io/agentscope/core/skill/util/SkillFileSystemHelper.java	Adds hidden/dotfile filtering during resource discovery when loading a skill.
agentscope-core/src/test/java/io/agentscope/core/skill/util/SkillFileSystemHelperTest.java	Adds coverage for filtering dot-prefixed files out of loaded resources.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ntscope/core/skill/util/SkillFileSystemHelper.java	90.90%	0 Missing and 1 partial ⚠️

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