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/en/common.json

@@ -21,7 +21,8 @@
     "remove": "Remove",
     "view": "View",
     "download": "Download",
-    "upload": "Upload"
+    "upload": "Upload",
+    "retry": "Retry"
   },
   "labels": {
     "loading": "Loading...",
@@ -135,5 +136,62 @@
     "maxFileSize": "Maximum file size: {{size}}",
     "uploading": "Uploading {{filename}} ({{current}}/{{total}})...",
     "uploadFailed": "Upload failed"
+  },
+  "reports": {
+    "weeklyPreview": {
+      "title": "Weekly Report Preview",
+      "generateNow": "Generate Now",
+      "generating": "Generating...",
+      "loading": "Loading report preview...",
+      "noData": "No report data available",
+      "noProjects": "No projects found",
+      "projects": "Projects",
+      "retry": "Retry",
+      "completedShort": "completed",
+      "done": "done",
+      "inProgressLower": "in progress",
+      "overdueLower": "overdue",
+      "blockedLower": "blocked",
+      "nextWeekLower": "next week",
+      "unassigned": "Unassigned",
+      "due": "Due",
+      "since": "Since",
+      "noReasonProvided": "No reason provided",
+      "daysOverdue": "{{count}} day overdue",
+      "daysOverdue_other": "{{count}} days overdue",
+      "status": {
+        "completed": "Completed",
+        "inProgress": "In Progress",
+        "overdue": "Overdue",
+        "blocked": "Blocked",
+        "nextWeek": "Next Week",
+        "total": "Total"
+      },
+      "errors": {
+        "loadFailed": "Failed to load report preview",
+        "generateFailed": "Failed to generate report"
+      },
+      "messages": {
+        "generateSuccess": "Report generated and notification sent!"
+      }
+    },
+    "history": {
+      "title": "Report History",
+      "loading": "Loading history...",
+      "retry": "Retry",
+      "empty": "No report history found. Reports are generated every Friday at 16:00.",
+      "totalReports": "{{count}} report",
+      "totalReports_other": "{{count}} reports",
+      "completed": "Completed",
+      "inProgress": "In Progress",
+      "overdue": "Overdue",
+      "status": {
+        "sent": "sent",
+        "failed": "failed"
+      },
+      "errors": {
+        "loadFailed": "Failed to load report history"
+      }
+    }
   }
 }