Examples 59/60/60a use a non-existent Anthropic model id

[ambiorix2099]

Files: examples/agents/59_coding_agent.py, examples/agents/60_github_coding_agent.py, examples/agents/60a_github_coding_agent_simple.py

Symptom: Run any of them → Agent execution FAILED, result: None, FinishReason.ERROR.

Cause: All three hardcode anthropic/claude-sonnet-4-20250514 (10 occurrences). The Anthropic API returns 404 not_found_error — that model does not exist. Visible only server-side, via the failed LLM_CHAT_COMPLETE task's reasonForIncompletion.

Fix: Replace with a current model id in all 10 places.

Verify: python examples/agents/59_coding_agent.py completes without execution FAILED.

[ambiorix2099]

Fixed by #495