feat: dashboard & report APIs with real DB stats

Backend:
- Add /dashboard/stats API (data_sources, tables, columns, labeled, sensitive, projects)
- Add /dashboard/distribution API (level/cat/source distribution, project progress, heatmap)
- Add /reports/stats API (total/auto/manual/reviewed counts + level distribution)
- Fix report download: add template relationship to ClassificationProject
- All stats computed from real DB queries

Frontend:
- Dashboard.vue: replace all hardcoded data with API-driven computed charts
- Report.vue: replace all hardcoded data with API-driven charts
- Add dashboard.ts and report.ts API clients

backend/app/api/v1/report.py

@@ -1,14 +1,46 @@
 from fastapi import APIRouter, Depends, Response
 from sqlalchemy.orm import Session
+from sqlalchemy import func
 
 from app.core.database import get_db
 from app.models.user import User
-from app.services import report_service
+from app.models.project import ClassificationResult, ClassificationProject
+from app.models.classification import Category, DataLevel
+from app.schemas.common import ResponseModel
 from app.api.deps import get_current_user
+from app.services import report_service
 
 router = APIRouter()
 
 
+@router.get("/stats")
+def get_report_stats(
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Global report statistics."""
+    total = db.query(ClassificationResult).count()
+    auto = db.query(ClassificationResult).filter(ClassificationResult.source == 'auto').count()
+    manual = db.query(ClassificationResult).filter(ClassificationResult.source == 'manual').count()
+    reviewed = db.query(ClassificationResult).filter(ClassificationResult.status == 'reviewed').count()
+
+    # Level distribution
+    level_dist = db.query(DataLevel.name, DataLevel.code, func.count(ClassificationResult.id)).\
+        join(ClassificationResult, DataLevel.id == ClassificationResult.level_id).\
+        group_by(DataLevel.id).order_by(DataLevel.sort_order).all()
+
+    return ResponseModel(data={
+        "total": total,
+        "auto": auto,
+        "manual": manual,
+        "reviewed": reviewed,
+        "level_distribution": [
+            {"name": name, "code": code, "count": count}
+            for name, code, count in level_dist
+        ],
+    })
+
+
 @router.get("/projects/{project_id}/download")
 def download_report(
     project_id: int,