fix(rectification): require three answers before uncertainty stop

One "一时说不好" no longer ends the interview. Plateau streaks use the
same sample floor. Delivery copy states why the range stopped.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/rectification-agentic/core/rectification-decision.ts

@@ -628,6 +628,7 @@ export function publicNextAction(decision: RectificationDecision): Readonly<{
   precision_stage: DerivedPrecisionStage;
   representative_time: string | null;
   credible_range: readonly [string, string] | null;
+  stop_reason: EvidenceStopReason | null;
 }> {
   return {
     type: decision.nextAction,
@@ -642,6 +643,7 @@ export function publicNextAction(decision: RectificationDecision): Readonly<{
     precision_stage: decision.precisionStage,
     representative_time: decision.representativeTime,
     credible_range: decision.credibleRange,
+    stop_reason: decision.stopReason ?? null,
   };
 }