feat(artifacts): list and download pipeline-run artifacts

[arseniy-pplx]

Summary

• extend tangle sdk artifacts get with --list, --out-dir, --only and --include-children
• accept a run id or root execution id for listing and fetching artifact output
• JSON-encode inline values as <name>.json; stream signed-URL content to a file with owner-only permissions on POSIX (0o600; Windows ACLs are not adjusted) under a sanitized artifact name
• refuse symlinks, collisions and path traversal; check the initial signed-URL host and every redirect hop against loopback, private, link-local and CGNAT address literals by default
• validate --query top-level and nested shapes (tasks/executions/components/artifact_ids) as clean CLI errors; null per-entry output filters mean all outputs (same as []), and an explicit --query '{}' is a valid empty query rather than a missing one
• add the public TangleApiClient.request_raw seam so artifact fetching does not depend on private client methods

Context

The current CLI reports artifact metadata but cannot retrieve artifact contents. This completes the pipeline-run output workflow while keeping large files streaming and applying conservative filesystem, redirect and error-redaction safeguards. Self-hosted deployments with private-network object storage can opt out with TANGLE_ALLOW_INTERNAL_ARTIFACT_HOSTS=1; the host-literal guard is a conservative default, not a DNS-rebinding defense.

Testing

• uv run pytest tests/test_artifacts.py tests/test_artifacts_cli.py tests/test_client.py
• uvx ruff check on the touched source files
• uv lock --check
• git diff --check