add day-detail view to monthly history calendar

날짜 셀 클릭 시 그 날 예정된 습관별 완료/실패/미완료 상태를 htmx로 불러와 보여준다.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/templates/history.html

@@ -32,8 +32,11 @@
     {% for d in week %}
     {% set summary = summary_map.get(d) %}
     <div
-      class="calendar-cell{{ '' if d.month == month else ' muted' }}"
+      class="calendar-cell clickable{{ '' if d.month == month else ' muted' }}"
       style="background: rgba(var(--color-accent-rgb), {{ heatmap_opacity(summary.checked_count, summary.scheduled_count) if summary else 0 }});"
+      hx-get="/history/day/{{ d.isoformat() }}"
+      hx-target="#day-detail"
+      hx-swap="innerHTML"
     >
       <span class="calendar-date">{{ d.day }}</span>
       {% if summary and summary.scheduled_count %}
@@ -45,6 +48,8 @@
   {% endfor %}
 </div>
 
+<div id="day-detail"></div>
+
 {% else %}
 <div class="card" style="overflow-x:auto;">
   <div style="display:flex; align-items:center; justify-content:space-between; margin-bottom: var(--space-2);">