fix(mcp): preserve remote health JSON

[gfargo]

Summary

• preserve valid degraded/unhealthy remote health JSON in MCP responses
• emit JSON-mode health output after on_health_fail hook chatter so the machine-readable result remains trailing
• remove only the exact run_remote_strut failure wrapper before retaining full jq validation
• keep plain SSH failures, malformed JSON, and arbitrary trailing diagnostics on the MCP error channel

Validation

• bats tests/ </dev/null — 2,650 passed, 2 expected skips
• bats tests/test_cmd_deploy.bats tests/test_cmd_status_remote.bats tests/test_mcp_tools.bats </dev/null — 140 passed
• direct MCP fixtures for unhealthy JSON, hook chatter, leading warnings, SSH failures, malformed JSON, contextual wrappers, and arbitrary suffix rejection
• shellcheck -x -S warning lib/cmd_deploy.sh lib/mcp/tools.sh
• bash -n lib/cmd_deploy.sh lib/mcp/tools.sh
• git diff --check
• semantic review — no actionable findings

Closes #509