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

tests/unit/lib/calendar/grid.test.ts

@@ -0,0 +1,175 @@
+import { describe, it, expect } from 'vitest';
+import {
+  toISODate,
+  parseISODate,
+  addDays,
+  addMonths,
+  startOfWeek,
+  getMonthGrid,
+  getWeekDays,
+  getDayHours,
+  eventDateKey,
+  eventHour,
+  formatTime,
+  eventsOnDay,
+  rangeForView,
+  stepAnchor,
+} from '@/lib/calendar/grid';
+
+describe('calendar/grid', () => {
+  describe('toISODate / parseISODate', () => {
+    it('toISODate formats a local date as YYYY-MM-DD', () => {
+      expect(toISODate(new Date(2026, 5, 15))).toBe('2026-06-15');
+      expect(toISODate(new Date(2026, 0, 9))).toBe('2026-01-09');
+    });
+
+    it('parseISODate round-trips through toISODate', () => {
+      const d = parseISODate('2026-06-15');
+      expect(toISODate(d)).toBe('2026-06-15');
+    });
+  });
+
+  describe('startOfWeek', () => {
+    it('returns the Sunday of the given date week', () => {
+      // 2026-06-17 is a Wednesday
+      expect(toISODate(startOfWeek(new Date(2026, 5, 17)))).toBe('2026-06-14');
+    });
+
+    it('returns the same date when already on Sunday', () => {
+      expect(toISODate(startOfWeek(new Date(2026, 5, 14)))).toBe('2026-06-14');
+    });
+  });
+
+  describe('getMonthGrid', () => {
+    it('produces full Sun-Sat weeks covering the month', () => {
+      // June 2026: 1st is Monday, 30th is Tuesday
+      const weeks = getMonthGrid(2026, 5);
+      for (const week of weeks) {
+        expect(week).toHaveLength(7);
+        expect(week[0].getDay()).toBe(0); // Sunday
+        expect(week[6].getDay()).toBe(6); // Saturday
+      }
+      // First cell is the Sunday on/before June 1 (May 31)
+      expect(toISODate(weeks[0][0])).toBe('2026-05-31');
+      // Last cell is the Saturday on/after June 30 (July 4)
+      expect(toISODate(weeks[weeks.length - 1][6])).toBe('2026-07-04');
+    });
+
+    it('starts on the 1st when the month begins on Sunday', () => {
+      // February 2026: 1st is a Sunday
+      const weeks = getMonthGrid(2026, 1);
+      expect(toISODate(weeks[0][0])).toBe('2026-02-01');
+    });
+
+    it('produces 4 to 6 weeks', () => {
+      const weeks = getMonthGrid(2026, 5);
+      expect(weeks.length).toBeGreaterThanOrEqual(4);
+      expect(weeks.length).toBeLessThanOrEqual(6);
+    });
+  });
+
+  describe('getWeekDays / getDayHours', () => {
+    it('returns 7 consecutive days Sunday-Saturday', () => {
+      const days = getWeekDays(new Date(2026, 5, 17));
+      expect(days).toHaveLength(7);
+      expect(toISODate(days[0])).toBe('2026-06-14');
+      expect(toISODate(days[6])).toBe('2026-06-20');
+    });
+
+    it('returns hours 0..23', () => {
+      expect(getDayHours()).toEqual(Array.from({ length: 24 }, (_, i) => i));
+    });
+  });
+
+  describe('addDays / addMonths', () => {
+    it('addDays moves the date', () => {
+      expect(toISODate(addDays(new Date(2026, 5, 15), 10))).toBe('2026-06-25');
+      expect(toISODate(addDays(new Date(2026, 5, 15), -15))).toBe('2026-05-31');
+    });
+
+    it('addMonths rolls over the year', () => {
+      expect(toISODate(addMonths(new Date(2026, 11, 15), 1))).toBe(
+        '2027-01-15'
+      );
+    });
+  });
+
+  describe('eventDateKey / eventHour / formatTime', () => {
+    it('eventDateKey takes the first 10 chars', () => {
+      expect(eventDateKey('2026-06-15T10:30:00')).toBe('2026-06-15');
+      expect(eventDateKey('2026-06-15')).toBe('2026-06-15');
+    });
+
+    it('eventHour returns the hour for timed events and null otherwise', () => {
+      expect(eventHour('2026-06-15T10:30:00')).toBe(10);
+      expect(eventHour('2026-06-15')).toBeNull();
+      expect(eventHour('2026-06-15T09:00:00')).toBe(9);
+    });
+
+    it('formatTime renders HH:mm or 終日', () => {
+      expect(formatTime('2026-06-15T10:30:00')).toBe('10:30');
+      expect(formatTime('2026-06-15')).toBe('終日');
+    });
+  });
+
+  describe('eventsOnDay', () => {
+    const events = [
+      { startAt: '2026-06-15T10:00:00', title: 'A' },
+      { startAt: '2026-06-15', title: 'B' },
+      { startAt: '2026-06-16T09:00:00', title: 'C' },
+    ];
+
+    it('filters events whose start date matches the day key', () => {
+      const result = eventsOnDay(events, '2026-06-15');
+      expect(result.map((e) => e.title)).toEqual(['A', 'B']);
+    });
+
+    it('returns empty when nothing matches', () => {
+      expect(eventsOnDay(events, '2026-07-01')).toHaveLength(0);
+    });
+  });
+
+  describe('rangeForView', () => {
+    it('day range covers a single day ending at T23:59:59', () => {
+      const r = rangeForView('day', new Date(2026, 5, 15));
+      expect(r).toEqual({ from: '2026-06-15', to: '2026-06-15T23:59:59' });
+    });
+
+    it('week range covers Sun-Sat ending at T23:59:59', () => {
+      const r = rangeForView('week', new Date(2026, 5, 17));
+      expect(r).toEqual({ from: '2026-06-14', to: '2026-06-20T23:59:59' });
+    });
+
+    it('month range covers the whole grid including overflow days', () => {
+      const r = rangeForView('month', new Date(2026, 5, 15));
+      expect(r.from).toBe('2026-05-31');
+      expect(r.to).toBe('2026-07-04T23:59:59');
+    });
+  });
+
+  describe('stepAnchor', () => {
+    it('steps months for month view', () => {
+      expect(toISODate(stepAnchor('month', new Date(2026, 5, 15), 1))).toBe(
+        '2026-07-15'
+      );
+      expect(toISODate(stepAnchor('month', new Date(2026, 5, 15), -1))).toBe(
+        '2026-05-15'
+      );
+    });
+
+    it('steps weeks for week view', () => {
+      expect(toISODate(stepAnchor('week', new Date(2026, 5, 17), 1))).toBe(
+        '2026-06-24'
+      );
+    });
+
+    it('steps days for day view', () => {
+      expect(toISODate(stepAnchor('day', new Date(2026, 5, 15), 1))).toBe(
+        '2026-06-16'
+      );
+      expect(toISODate(stepAnchor('day', new Date(2026, 5, 15), -1))).toBe(
+        '2026-06-14'
+      );
+    });
+  });
+});