feat: 일정 주간/월간 뷰 전환 추가

상단 토글(주간/월간)로 보기 전환. 월간은 전통 달력 그리드(주×요일).

- scheduleDate: firstOfMonth/addMonths/monthLabel/monthGridWeeks(+MonthDay) 추가
- schedule.store: viewMode + anchor 기반으로 주간/월간 범위·라벨·네비 일원화
  (goPrev/goNext 가 모드별로 주/월 이동, setViewMode 시 범위 재조회)
- ScheduleMonthGrid: 주 단위 다중일 막대(레인 패킹) + 초과 '+N',
  카테고리 색·유형 필터·오늘/주말/이전·다음달 표기, 막대 클릭 시 상세 패널
- SchedulePage: SegmentedTabs 토글 + 주간/월간 조건부 렌더

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/pages/relay/SchedulePage.vue

@@ -1,13 +1,15 @@
 <script setup lang="ts">
-// 일정 — 전사 공유 주간 타임라인(간트형) 캘린더
+// 일정 — 전사 공유 캘린더(주간 간트 / 월간 달력 그리드 전환)
 import { computed, onMounted, ref } from 'vue'
 import AppShell from '@/layouts/AppShell.vue'
 import ScheduleTimeline from '@/components/schedule/ScheduleTimeline.vue'
+import ScheduleMonthGrid from '@/components/schedule/ScheduleMonthGrid.vue'
 import ScheduleDetailPanel from '@/components/schedule/ScheduleDetailPanel.vue'
 import ScheduleEventModal from '@/components/schedule/ScheduleEventModal.vue'
 import ScheduleCategoryModal from '@/components/schedule/ScheduleCategoryModal.vue'
 import ScheduleTypeFilter from '@/components/schedule/ScheduleTypeFilter.vue'
-import { useScheduleStore } from '@/stores/schedule.store'
+import SegmentedTabs from '@/components/common/SegmentedTabs.vue'
+import { useScheduleStore, type ScheduleViewMode } from '@/stores/schedule.store'
 import { useDialogStore } from '@/stores/dialog.store'
 import type {
   ApiScheduleEvent,
@@ -18,6 +20,12 @@ import type {
 const store = useScheduleStore()
 const dialog = useDialogStore()
 
+// 보기 모드 토글 옵션
+const VIEW_OPTIONS: { value: ScheduleViewMode; label: string }[] = [
+  { value: 'week', label: '주간' },
+  { value: 'month', label: '월간' },
+]
+
 const selId = ref<string | null>(null)
 const eventModal = ref<{ init: ApiScheduleEvent | null } | null>(null)
 const catModal = ref<{ init: import('@/types/schedule').ApiScheduleCategory | null } | null>(null)
@@ -107,8 +115,8 @@ async function onDeleteCategory(id: string): Promise<void> {
           <div class="navgroup">
             <button
               class="navbtn"
-              title="이전 주"
-              @click="store.goPrevWeek()"
+              :title="store.viewMode === 'week' ? '이전 주' : '이전 달'"
+              @click="store.goPrev()"
             >
               <svg
                 viewBox="0 0 24 24"
@@ -121,8 +129,8 @@ async function onDeleteCategory(id: string): Promise<void> {
             </button>
             <button
               class="navbtn"
-              title="다음 주"
-              @click="store.goNextWeek()"
+              :title="store.viewMode === 'week' ? '다음 주' : '다음 달'"
+              @click="store.goNext()"
             >
               <svg
                 viewBox="0 0 24 24"
@@ -136,6 +144,11 @@ async function onDeleteCategory(id: string): Promise<void> {
           </div>
           <span class="range">{{ store.rangeLabel }}</span>
         </div>
+        <SegmentedTabs
+          :model-value="store.viewMode"
+          :options="VIEW_OPTIONS"
+          @update:model-value="store.setViewMode"
+        />
         <div class="spacer" />
         <ScheduleTypeFilter
           :categories="store.categories"
@@ -166,6 +179,7 @@ async function onDeleteCategory(id: string): Promise<void> {
       <div class="content-row">
         <div class="viewport">
           <ScheduleTimeline
+            v-if="store.viewMode === 'week'"
             :categories="store.categories"
             :events="store.events"
             :days="store.days"
@@ -174,6 +188,15 @@ async function onDeleteCategory(id: string): Promise<void> {
             @select="selId = $event"
             @add-category="openNewCategory"
           />
+          <ScheduleMonthGrid
+            v-else
+            :weeks="store.monthWeeks"
+            :events="store.events"
+            :categories="store.categories"
+            :active-type-ids="store.activeTypeIds"
+            :sel-id="selId"
+            @select="selId = $event"
+          />
         </div>
         <div
           v-if="selEvent"