Propagate "Execution model" note to other long-running skills

[MacAttak]

Context

Follow-up from #146. That PR added an "Execution model" Constraints block to sw-build clarifying that "autonomous" means within-turn unattended decision-making, not detached background execution, and that the Skill tool has no run_in_background parameter.

The canonical definition was also added to protocols/decision.md, but skills load that protocol on demand at decision points — not at skill start. A model that jumps straight to a skill's Constraints block can still hallucinate the background parameter before it ever consults decision.md.

Affected skills

Other skills that open with "Operates autonomously" framing in the Goal block:

• core/skills/sw-plan/SKILL.md
• core/skills/sw-research/SKILL.md
• core/skills/sw-design/SKILL.md
• core/skills/sw-verify/SKILL.md

Options

1. Copy the same Execution model (LOW freedom) Constraints paragraph into each of the four skills above (simple, redundant).
2. Extract the paragraph into a shared snippet (e.g. protocols/execution-model.md or inline include) and reference it from all five skills (DRY, but adds an indirection).

Acceptance criteria

• Each affected skill states that it runs in the foreground in the same turn the slash command was invoked.
• Each affected skill states that the Skill tool has no run_in_background parameter.
• The note is reachable from the Constraints block without first loading another protocol.
• protocols/headless.md cross-reference preserved for the CI/CD path.

Origin

Reviewer (claude[bot]) suggestion on #146:
#146 (comment)