Sync OSS release snapshot 2.4.3

[keshprad]

Summary

• Refresh the public SkillSpector snapshot from internal release release/oss-2026-07-22 at 187336ab94ec2319cbefe987084034331a5709db.
• Publish version 2.4.3 and its public-safe changelog entry.
• Synchronize the suppression matching fix and Anthropic endpoint-policy updates now present in internal main.

Diff notes

• 10 public files changed; no GitHub-only files or directories were deleted.
• The snapshot retains public workflows and excludes internal release, CI, Sonar, review-tooling, and NVIDIA Inference provider paths.

Verification

• PYTHONPATH=src make test-unit
• ruff check src tests
• ruff format --check src tests
• git diff --check origin/main
• GitNexus change detection: medium risk, one affected suppression-report flow

[psvaggelis]

Heads-up: this snapshot reverted #282 (merged into main 2026-07-22). It restored providers/anthropic/provider.py and its three test files to their pre-fix state, so AnthropicProvider no longer honors ANTHROPIC_BASE_URL on current main. #301 re-applies it.