Preserve stdout in CLI failure errors

[abhinavgautam01]

Fixes #2

Summary

Fixes _wrap_cli so fallback command_failed responses preserve useful stdout context when a backing CLI exits with an error.

Previously, _wrap_cli parsed stderr for structured error envelopes, but if stderr was not valid JSON it returned a generic command_failed response and discarded stdout entirely. Some CLIs print hints, diagnostics or relevant failure details to stdout, so dropping it made failures harder for MCP clients and agents to debug.

Changes

• Include bounded stdout in fallback command_failed error details when present
• Keep existing structured stderr error-envelope behavior unchanged
• Add a regression test covering stdout preservation on CLI failure

Validation

• PYTHONPATH=src pytest -q
• python3 -m compileall -q src tests
• git diff --check
• CI denylist guard scan
• CI secret-pattern scan