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>

tests/web/test_dashboard_summary.py

@@ -0,0 +1,43 @@
+from datetime import datetime, timedelta, timezone
+
+from app.db.models import HealthState, SyncRunStatus
+from app.db.repositories import SyncRunRepository, UserRepository
+
+
+def _seed_user(session, name, *, enabled=True, health_state=HealthState.HEALTHY):
+    return UserRepository(session).create(
+        name=name,
+        enabled=enabled,
+        health_state=health_state,
+        mywhoosh_email_enc=f"mw-{name}",
+        mywhoosh_password_enc=f"mw-pw-{name}",
+        garmin_email_enc=f"g-{name}",
+        garmin_password_enc=f"g-pw-{name}",
+    )
+
+
+def test_dashboard_shows_summary_tiles(app, authenticated_client) -> None:
+    with app.state.session_factory() as session:
+        alex = _seed_user(session, "Alex", enabled=True)
+        _seed_user(session, "Jamie", enabled=False, health_state=HealthState.ACTION_REQUIRED)
+
+        run_repo = SyncRunRepository(session)
+        run = run_repo.start(alex.id)
+        run.started_at = datetime.now(timezone.utc) - timedelta(hours=2)
+        run_repo.finish(run.id, status=SyncRunStatus.SUCCESS, discovered=3, imported=3, skipped=0, failed=0)
+
+    response = authenticated_client.get("/")
+
+    assert response.status_code == 200
+    assert '<span class="stat-tile-value">2</span>' in response.text
+    assert "1 enabled" in response.text
+    assert '<span class="stat-tile-value">3</span>' in response.text
+    assert '<span class="stat-tile-value">100%</span>' in response.text
+    assert '<span class="stat-tile-value">1</span>' in response.text
+
+
+def test_dashboard_shows_dash_for_success_rate_without_recent_runs(authenticated_client) -> None:
+    response = authenticated_client.get("/")
+
+    assert response.status_code == 200
+    assert '<span class="stat-tile-value">&ndash;</span>' in response.text