v10.25: proactive goal surfacing and response style

• make candidate-goal surfacing more proactive at real decision boundaries when several next slices remain live
• refine default non-trivial answer style to be easy-first, compact-but-complete, scanable, identifier-meaning-first, evidence-layer-clear, and decision-ready
• add playground case 17 for proactive goal surfacing and decision-ready explanation while keeping playground non-runtime