feat(V2-6차): 테마 토글 + Mermaid + 오디오 재생 + Dashboard 차트

[A] Dark/Light/6종 + Auto 테마 토글
- theme-mode-context.tsx: localStorage 영속 + prefers-color-scheme
- theme-provider.tsx: 컨텍스트 기반 동적 getTheme
- sidebar.tsx: MUI Select 토글 (PaletteIcon)
- 12개 locale theme.* 키 추가 (label/dark/light/auto/nord/solarized/catppuccin/dracula)

[B] DocumentEditor Mermaid + Markdown 렌더
- markdown-preview.tsx: react-markdown + remark-gfm + lazy mermaid
  - mermaid 코드 블록 자동 SVG 렌더
  - dark theme + d3ro 폰트
- document-editor.tsx: Edit/Preview Tabs

[C] 회의 오디오 재생
- meeting-audio-player.tsx: Supabase Storage signed URL (1h) → <audio controls>
- meetings/[id] AUDIO 카드 추가

[D] Dashboard 14일 추이 차트
- meetings-trend-chart.tsx: recharts LineChart (회의/문서)
- dashboard/page.tsx: 14일 데이터 집계 + 이번 주 stat 자동 계산

[W] fix: Emotion key 'd3ro-mui' → 'mui'
- 'd3ro-mui'에 숫자 3이 포함돼 Emotion 키 검증 실패
- dev SSR /login 500 에러 차단했음

deps:
- react-markdown@10, remark-gfm@4, mermaid@11, recharts@3

apps/web/src/components/dashboard/meetings-trend-chart.tsx

@@ -0,0 +1,83 @@
+'use client'
+
+// apps/web/src/components/dashboard/meetings-trend-chart.tsx
+// recharts 기반 회의/문서 추이 차트 (최근 14일).
+
+import {
+  ResponsiveContainer,
+  LineChart,
+  Line,
+  XAxis,
+  YAxis,
+  Tooltip,
+  CartesianGrid,
+  Legend
+} from 'recharts'
+import { Box } from '@mui/material'
+import { d3roPalette } from '@d3ro/ui/theme'
+
+export interface TrendPoint {
+  date: string
+  meetings: number
+  documents: number
+}
+
+interface MeetingsTrendChartProps {
+  points: TrendPoint[]
+}
+
+export function MeetingsTrendChart({ points }: MeetingsTrendChartProps): React.ReactElement {
+  return (
+    <Box sx={{ width: '100%', height: 260 }}>
+      <ResponsiveContainer width="100%" height="100%">
+        <LineChart data={points} margin={{ top: 5, right: 12, left: -12, bottom: 5 }}>
+          <CartesianGrid strokeDasharray="3 3" stroke={d3roPalette.border.subtle} />
+          <XAxis
+            dataKey="date"
+            stroke={d3roPalette.text.muted}
+            fontSize={11}
+            tickLine={false}
+          />
+          <YAxis
+            stroke={d3roPalette.text.muted}
+            fontSize={11}
+            tickLine={false}
+            allowDecimals={false}
+          />
+          <Tooltip
+            contentStyle={{
+              backgroundColor: d3roPalette.bg.elevated,
+              border: `1px solid ${d3roPalette.border.default}`,
+              borderRadius: 8,
+              color: d3roPalette.text.primary,
+              fontSize: 12
+            }}
+            labelStyle={{ color: d3roPalette.text.label }}
+          />
+          <Legend
+            wrapperStyle={{ fontSize: 11, color: d3roPalette.text.secondary }}
+            iconType="circle"
+          />
+          <Line
+            type="monotone"
+            dataKey="meetings"
+            name="Meetings"
+            stroke={d3roPalette.accent.amber}
+            strokeWidth={2}
+            dot={{ r: 3 }}
+            activeDot={{ r: 5 }}
+          />
+          <Line
+            type="monotone"
+            dataKey="documents"
+            name="Documents"
+            stroke={d3roPalette.tag.purple}
+            strokeWidth={2}
+            dot={{ r: 3 }}
+            activeDot={{ r: 5 }}
+          />
+        </LineChart>
+      </ResponsiveContainer>
+    </Box>
+  )
+}