Add dashboard summary tiles

Shows rider count, activities imported in the last 7 days, 7-day
sync success rate, and how many riders currently need attention,
right above the rider list where an admin looks first.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/web/routes.py

@@ -1,3 +1,4 @@
+from datetime import timedelta
 from pathlib import Path
 
 from fastapi import APIRouter, Form, HTTPException, Request, status
@@ -6,11 +7,13 @@ from fastapi.templating import Jinja2Templates
 
 from app.auth.admin import password_matches, require_admin
 from app.auth.csrf import ensure_csrf_token, validate_csrf
-from app.db.models import SyncUser
+from app.db.models import SyncUser, utcnow
 from app.db.repositories import ActivityRepository, SyncRunRepository, UserRepository
 from app.security.credentials import CredentialCipher
 from app.web.forms import UserFormData
 
+DASHBOARD_SUMMARY_WINDOW = timedelta(days=7)
+
 router = APIRouter()
 templates = Jinja2Templates(directory=str(Path(__file__).resolve().parent / "templates"))
 
@@ -70,11 +73,13 @@ def login(
 def dashboard(request: Request):
     require_admin(request)
     with request.app.state.session_factory() as session:
-        rows = UserRepository(session).dashboard_rows()
+        repository = UserRepository(session)
+        rows = repository.dashboard_rows()
+        summary = repository.dashboard_summary(since=utcnow() - DASHBOARD_SUMMARY_WINDOW)
         return templates.TemplateResponse(
             request,
             "dashboard.html",
-            {"rows": rows, "csrf_token": ensure_csrf_token(request)},
+            {"rows": rows, "summary": summary, "csrf_token": ensure_csrf_token(request)},
         )