feat(spawn): add per-invocation --effort

[hmirin]

Summary

• add first-class spawn.sh --effort <level> support
• map effort to each direct CLI through type-manifest fields
• reject unsupported direct CLI types and launcher-owned configurations instead of silently ignoring the option

Why

spawn_options.yaml applies one static set of flags per agent type. An orchestrator that chooses a different effort for each worker therefore needs to generate a temporary config or maintain a wrapper around spawn.sh.

--model already provides a per-invocation, pass-through contract. This adds the equivalent contract for effort, so callers can express the complete worker launch directly:

/agmsg spawn codex reviewer --model gpt-5 --effort xhigh

Design

• Effort levels are passed through unchecked; the target CLI remains responsible for validation.
• Claude declares effort_arg=--effort and receives --effort high.
• Codex declares effort_arg=-c plus effort_value_prefix=model_reasoning_effort= and receives -c model_reasoning_effort=xhigh.
• Types without effort_arg fail clearly.
• Node launchers continue to own their model and effort configuration.
• Terminal and tmux placement behavior is unchanged.

Validation

• effort-focused Bats tests: 7/7 passed locally
• bash -n scripts/spawn.sh
• git diff --check origin/main
• checked current Claude and Codex CLI help, including Codex's resumed-session -c argument placement