Add categorize-and-probe helpers for shell spawn failures, expose
gitea_diagnose_terminal, and fail closed on mutation capability resolve
when the terminal launcher is unhealthy (BLOCKED + DIAGNOSE). Document
the operator path in the workflow runbooks.
Enforce native MCP-first paths for Gitea mutations with fail-closed
assessment helpers, shell spawn circuit breaker tracking, and MCP tools
for operation-path assessment and shell health reporting.
Closes#270