fix: filter hidden artifacts from LLM context

[Hughhhhcoder]

Fixes #6873

Summary

• add an optional sync/async artifact-name filter to LoadArtifactsTool
• apply the filter to the tool response, dynamic instructions, and artifact content loading
• preserve existing behavior when no filter is configured

Tests

• uv run pytest tests/unittests/tools/test_load_artifacts_tool.py -q
• uv run pre-commit run --files src/google/adk/tools/load_artifacts_tool.py tests/unittests/tools/test_load_artifacts_tool.py

[google-cla]

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[Hughhhhcoder]

Thanks for the update. The code and repository checks are passing; the only failing check is the Google CLA check, which requires the contributor to complete the CLA at the link provided by the bot before maintainers can review. No code change is needed for this CI failure.

[Hughhhhcoder]

Thanks — I’ve completed the Google CLA and triggered the rescan. The cla/google check is now passing, and all remaining checks are passing or skipped. The PR is ready for maintainer review.

[Hughhhhcoder]

The latest Continuous Integration and Do Not Merge on GitHub pull-request runs are completed with action_required, while cla/google and the target checks pass or are skipped. Could a maintainer approve these workflows when convenient so the PR can proceed to review?