feat(inbox): ContinuityBadge with recovery-friendly copy

Task 23 of the slice plan. Reads continuity from the zustand
store and renders one of three states: '이번 주 한 줄이면
시작입니다' (0 notes), '이번 주 N/7' (in-progress), or
'이번 주 7/7 ✓ · 연속 K주 완성' (target hit, with K only when
> 0). No '실패'/'끊김' wording.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/renderer/inbox/components/ContinuityBadge.tsx

@@ -1,2 +1,25 @@
 import React from 'react';
-export function ContinuityBadge() { return null; }
+import { useInbox } from '../store.js';
+
+export function ContinuityBadge(): React.ReactElement | null {
+  const c = useInbox((s) => s.continuity);
+  if (!c.weekStart) return null;
+  if (c.weekCount === 0) {
+    return <div style={{ fontSize: 13, color: '#666' }}>이번 주 한 줄이면 시작입니다</div>;
+  }
+  if (c.weekCount < c.weekTarget) {
+    return (
+      <div style={{ fontSize: 13, color: '#444' }}>
+        이번 주 <b>{c.weekCount}/{c.weekTarget}</b>
+      </div>
+    );
+  }
+  return (
+    <div style={{ fontSize: 13, color: '#236b1a' }}>
+      이번 주 <b>{c.weekCount}/{c.weekTarget}</b> ✓
+      {c.consecutiveCompleteWeeks > 0 && (
+        <span style={{ color: '#888' }}> · 연속 {c.consecutiveCompleteWeeks}주 완성</span>
+      )}
+    </div>
+  );
+}