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/Auth/ICertProvisioningService.cs

@@ -0,0 +1,25 @@
+namespace SharepointToolbox.Web.Services.Auth;
+
+/// <summary>
+/// Public material of a freshly generated app-only certificate. The private key is already
+/// stored (encrypted) in the cert store; these fields are what the app registration needs
+/// to trust the certificate as a sign-in credential.
+/// </summary>
+/// <param name="Thumbprint">SHA-1 thumbprint of the generated certificate.</param>
+/// <param name="PublicCertBase64">Base64 of the DER-encoded public certificate (Graph keyCredential.key).</param>
+/// <param name="NotBefore">Validity start (UTC).</param>
+/// <param name="NotAfter">Validity end (UTC).</param>
+public record CertProvisioningResult(
+    string Thumbprint,
+    string PublicCertBase64,
+    DateTimeOffset NotBefore,
+    DateTimeOffset NotAfter);
+
+/// <summary>
+/// Generates a self-signed certificate for a client profile, stores the private key in the
+/// app-only cert store, and returns the public material to register against the Entra app.
+/// </summary>
+public interface ICertProvisioningService
+{
+    Task<CertProvisioningResult> GenerateAndStoreAsync(string profileId, string subjectName, CancellationToken ct = default);
+}