feat: implement debug logging cleanup and i18n coverage proposals

## cleanup-debug-logging
- Create environment-aware logger utility (logger.ts)
- Replace 60+ console.log/error statements across 28 files
- Production: only warn/error logs visible
- Development: all log levels with prefixes

Updated files:
- Contexts: NotificationContext, ProjectSyncContext, AuthContext
- Components: GanttChart, CalendarView, ErrorBoundary, and 11 others
- Pages: Tasks, Projects, Dashboard, and 7 others
- Services: api.ts

## complete-i18n-coverage
- WeeklyReportPreview: all strings translated, dynamic locale
- ReportHistory: all strings translated, dynamic locale
- AuditPage: detail modal and verification modal translated
- WorkloadPage: error message translated

Locale files updated:
- en/common.json, zh-TW/common.json: reports section
- en/audit.json, zh-TW/audit.json: modal sections
- en/workload.json, zh-TW/workload.json: errors section

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/public/locales/zh-TW/common.json

@@ -21,7 +21,8 @@
     "remove": "移除",
     "view": "檢視",
     "download": "下載",
-    "upload": "上傳"
+    "upload": "上傳",
+    "retry": "重試"
   },
   "labels": {
     "loading": "載入中...",
@@ -135,5 +136,60 @@
     "maxFileSize": "檔案大小上限：{{size}}",
     "uploading": "正在上傳 {{filename}} ({{current}}/{{total}})...",
     "uploadFailed": "上傳失敗"
+  },
+  "reports": {
+    "weeklyPreview": {
+      "title": "週報預覽",
+      "generateNow": "立即產生",
+      "generating": "產生中...",
+      "loading": "載入報告預覽中...",
+      "noData": "無可用的報告資料",
+      "noProjects": "找不到專案",
+      "projects": "專案",
+      "retry": "重試",
+      "completedShort": "已完成",
+      "done": "完成",
+      "inProgressLower": "進行中",
+      "overdueLower": "逾期",
+      "blockedLower": "受阻",
+      "nextWeekLower": "下週",
+      "unassigned": "未指派",
+      "due": "截止",
+      "since": "自",
+      "noReasonProvided": "未提供原因",
+      "daysOverdue": "逾期 {{count}} 天",
+      "status": {
+        "completed": "已完成",
+        "inProgress": "進行中",
+        "overdue": "逾期",
+        "blocked": "受阻",
+        "nextWeek": "下週",
+        "total": "總計"
+      },
+      "errors": {
+        "loadFailed": "載入報告預覽失敗",
+        "generateFailed": "產生報告失敗"
+      },
+      "messages": {
+        "generateSuccess": "報告已產生並發送通知！"
+      }
+    },
+    "history": {
+      "title": "報告歷史",
+      "loading": "載入歷史中...",
+      "retry": "重試",
+      "empty": "找不到報告歷史記錄。報告會在每週五 16:00 自動產生。",
+      "totalReports": "{{count}} 份報告",
+      "completed": "已完成",
+      "inProgress": "進行中",
+      "overdue": "逾期",
+      "status": {
+        "sent": "已發送",
+        "failed": "失敗"
+      },
+      "errors": {
+        "loadFailed": "載入報告歷史失敗"
+      }
+    }
   }
 }