Add scheduled reports + app-only cert auth; fix tenant-wide user-access audit

Feature work:
- Certificate (app-only) auth per profile: cert store, context/Graph client
  factories, automated app-registration provisioning (delegated + application
  permissions, admin consent), and a SessionManager seam that resolves the auth
  model per profile.
- Scheduled reports: repositories, hosted service/runner/coordinator, report
  pages, and email delivery (app-only Mail.Send).
- Tenant-wide user-access audit when no site is selected.

Audit fixes:
- Site enumeration: app-only discovery used Graph getAllSites (needs Graph
  Sites.Read.All the cert app lacks) and silently returned empty. Switched to
  the admin-host CSOM TenantSiteEnumerator, matching the scheduler; both auth
  models now share one enumeration path.
- Group expansion: the scan records a SharePoint group as a single principal, so
  user-centric audits found nothing for group-granted access. Resolve group
  membership (shared by audit + scheduler) and attribute it to the target user.
- M365 group claims: the resolver only recognized AAD security groups
  (c:0t.c|). Group-connected/Teams sites grant via the M365 group claim
  (c:0o.c|…|<guid>[_o]); now expanded too, resolving owners for the "_o" claim.
- Provision Directory.Read.All as an application permission so M365/AAD group
  expansion works under the cert identity.

Also: ignore data/appcerts/ (encrypted certificate key material).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Services/Reports/IReportMailService.cs

@@ -0,0 +1,21 @@
+using SharepointToolbox.Web.Core.Models;
+
+namespace SharepointToolbox.Web.Services.Reports;
+
+/// <summary>Sends a generated report as a Graph email (app-only, Mail.Send).</summary>
+public interface IReportMailService
+{
+    /// <summary>
+    /// Sends <paramref name="bytes"/> as an attachment to the recipients in
+    /// <paramref name="settings"/>, sending AS <see cref="ReportEmailSettings.From"/>.
+    /// Subject/body placeholders are resolved from the schedule and client.
+    /// </summary>
+    Task SendAsync(
+        TenantProfile profile,
+        ScheduledReport schedule,
+        ReportEmailSettings settings,
+        string fileName,
+        string mime,
+        byte[] bytes,
+        CancellationToken ct = default);
+}