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>

Infrastructure/Auth/IAppOnlyContextFactory.cs

@@ -0,0 +1,47 @@
+using Azure.Core;
+using Microsoft.Graph;
+using Microsoft.SharePoint.Client;
+using SharepointToolbox.Web.Core.Models;
+
+namespace SharepointToolbox.Web.Infrastructure.Auth;
+
+/// <summary>
+/// Builds app-only (certificate-based) clients for a client profile. Drives BOTH the
+/// background report scheduler AND the interactive session: when a profile is configured
+/// for certificate auth (see <see cref="IsConfigured"/>), technicians operate through the
+/// app identity and never sign in to SharePoint per profile. Requires
+/// <see cref="TenantProfile.AppOnlyEnabled"/>, an app-only client id, and a stored certificate.
+/// </summary>
+public interface IAppOnlyContextFactory
+{
+    /// <summary>
+    /// True when this profile can authenticate app-only without an interactive sign-in:
+    /// <see cref="TenantProfile.AppOnlyEnabled"/> is set, an app-only client id is present,
+    /// and a certificate is stored for the profile. When false, callers fall back to the
+    /// delegated refresh-token flow.
+    /// </summary>
+    bool IsConfigured(TenantProfile profile);
+
+    /// <summary>CSOM context for a specific site, authenticated app-only.</summary>
+    Task<ClientContext> CreateContextAsync(TenantProfile profile, string siteUrl, CancellationToken ct = default);
+
+    /// <summary>Microsoft Graph client, authenticated app-only.</summary>
+    Task<GraphServiceClient> CreateGraphClientAsync(TenantProfile profile, CancellationToken ct = default);
+
+    /// <summary>Acquires an app-only access token for an arbitrary scope (e.g. a SharePoint host or Graph).</summary>
+    Task<AccessToken> GetTokenAsync(TenantProfile profile, string scope, CancellationToken ct = default);
+
+    /// <summary>
+    /// Verifies the stored credentials can authenticate against the tenant root web.
+    /// Returns null on success, or an error message describing the failure.
+    /// </summary>
+    Task<string?> TestConnectionAsync(TenantProfile profile, CancellationToken ct = default);
+
+    /// <summary>
+    /// Polls <see cref="TestConnectionAsync"/> until it succeeds or <paramref name="timeout"/>
+    /// elapses. After a fresh app registration, the certificate key credential and app-role
+    /// admin consent take time to propagate through Entra (token requests 401 until then);
+    /// this waits that window out. Returns null once ready, or the last error on timeout.
+    /// </summary>
+    Task<string?> WaitUntilReadyAsync(TenantProfile profile, TimeSpan timeout, CancellationToken ct = default);
+}