feat(calendar): replace list view with month/week/day grid + date detail dialog

カレンダー画面を一覧表示から実際のカレンダーグリッドへ変更。

- lib/calendar/grid.ts: 月グリッド/週/時間グリッド/取得範囲(rangeForView)の純粋な日付ヘルパー (+22 unit tests)
- components/calendar/: CalendarView(月/週/日 切替・prev/next/今日)・MonthView(truncateチップ)・WeekView・DayView(時間グリッド+終日)・EventDetailDialog(詳細・フォーカス管理)・sourceColors
- page.tsx: view/date searchParamsから範囲を計算しServer Componentで取得、CalendarViewへ渡す
- e2e: 表示切替・詳細ダイアログ・ナビステップ(週=7日/日=1日)を追加

components/calendar/MonthView.tsx

@@ -0,0 +1,105 @@
+'use client';
+
+import type { CalendarEventView } from '@/services/ScheduleService';
+import { eventsOnDay, toISODate } from '@/lib/calendar/grid';
+import {
+  SOURCE_COLORS,
+  SOURCE_CHIP_BORDER,
+  WEEKDAY_LABELS,
+} from '@/components/calendar/sourceColors';
+
+const MAX_VISIBLE_CHIPS = 3;
+
+/**
+ * 月表示グリッド。日曜始まりの7列グリッドで各日にイベントチップを表示する。
+ * 長いタイトルは truncate し、3件を超える分は「+N件」でまとめる。
+ */
+export function MonthView({
+  events,
+  weeks,
+  anchorMonth,
+  todayKey,
+  onSelectDate,
+}: {
+  events: CalendarEventView[];
+  weeks: Date[][];
+  anchorMonth: number;
+  todayKey: string;
+  onSelectDate: (dateKey: string) => void;
+}) {
+  return (
+    <div className="overflow-hidden rounded-lg border bg-white">
+      <div className="grid grid-cols-7 border-b bg-gray-50 text-center text-xs font-medium text-gray-500">
+        {WEEKDAY_LABELS.map((w) => (
+          <div key={w} className="py-2">
+            {w}
+          </div>
+        ))}
+      </div>
+      <div>
+        {weeks.map((week, wi) => (
+          <div key={wi} className="grid grid-cols-7 border-b last:border-b-0">
+            {week.map((day) => {
+              const key = toISODate(day);
+              const dayEvents = eventsOnDay(events, key);
+              const inMonth = day.getMonth() === anchorMonth;
+              const isToday = key === todayKey;
+              const visible = dayEvents.slice(0, MAX_VISIBLE_CHIPS);
+              const hidden = dayEvents.length - visible.length;
+              return (
+                <div
+                  key={key}
+                  className={`min-h-[110px] border-r border-t p-1 last:border-r-0 ${
+                    inMonth ? 'bg-white' : 'bg-gray-50'
+                  }`}
+                  data-testid={`calendar-day-${key}`}
+                >
+                  <button
+                    type="button"
+                    onClick={() => onSelectDate(key)}
+                    className={`flex h-6 w-6 items-center justify-center rounded-full text-xs ${
+                      isToday
+                        ? 'bg-blue-600 font-bold text-white'
+                        : inMonth
+                          ? 'text-gray-700 hover:bg-gray-100'
+                          : 'text-gray-300 hover:bg-gray-100'
+                    }`}
+                    aria-label={`${key} の詳細を開く`}
+                  >
+                    {day.getDate()}
+                  </button>
+                  <div className="mt-1 space-y-0.5">
+                    {visible.map((e) => (
+                      <button
+                        key={e.key}
+                        type="button"
+                        onClick={() => onSelectDate(key)}
+                        title={e.title}
+                        className={`block w-full truncate rounded border px-1 text-left text-xs ${
+                          SOURCE_COLORS[e.source] ?? 'bg-gray-100 text-gray-600'
+                        } ${SOURCE_CHIP_BORDER[e.source] ?? 'border-gray-200'}`}
+                        data-testid={`calendar-event-${e.key}`}
+                      >
+                        {e.title}
+                      </button>
+                    ))}
+                    {hidden > 0 && (
+                      <button
+                        type="button"
+                        onClick={() => onSelectDate(key)}
+                        aria-label={`${key}の残り${hidden}件を開く`}
+                        className="block w-full truncate text-left text-xs text-gray-400 hover:text-gray-600"
+                      >
+                        +{hidden}件
+                      </button>
+                    )}
+                  </div>
+                </div>
+              );
+            })}
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}