feat(08-01): add SimplifiedPermissionEntry wrapper and PermissionSummary model

- SimplifiedPermissionEntry wraps PermissionEntry with computed labels and risk level
- Passthrough properties preserve DataGrid binding compatibility
- PermissionSummary record for grouped risk-level counts
- PermissionSummaryBuilder always returns all 4 risk levels for consistent UI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SharepointToolbox/Core/Models/PermissionSummary.cs

@@ -0,0 +1,64 @@
+namespace SharepointToolbox.Core.Models;
+
+/// <summary>
+/// Summary counts of permission entries grouped by risk level.
+/// Displayed in the summary panel when simplified mode is active.
+/// </summary>
+public record PermissionSummary(
+    /// <summary>Label for this group (e.g. "High Risk", "Read Only").</summary>
+    string Label,
+    /// <summary>The risk level this group represents.</summary>
+    RiskLevel RiskLevel,
+    /// <summary>Number of permission entries at this risk level.</summary>
+    int Count,
+    /// <summary>Number of distinct users at this risk level.</summary>
+    int DistinctUsers
+);
+
+/// <summary>
+/// Computes PermissionSummary groups from SimplifiedPermissionEntry collections.
+/// </summary>
+public static class PermissionSummaryBuilder
+{
+    /// <summary>
+    /// Risk level display labels.
+    /// </summary>
+    private static readonly Dictionary<RiskLevel, string> Labels = new()
+    {
+        [RiskLevel.High] = "High Risk",
+        [RiskLevel.Medium] = "Medium Risk",
+        [RiskLevel.Low] = "Low Risk",
+        [RiskLevel.ReadOnly] = "Read Only",
+    };
+
+    /// <summary>
+    /// Builds summary counts grouped by risk level from a collection of simplified entries.
+    /// Always returns all 4 risk levels, even if count is 0, for consistent UI binding.
+    /// </summary>
+    public static IReadOnlyList<PermissionSummary> Build(
+        IEnumerable<SimplifiedPermissionEntry> entries)
+    {
+        var grouped = entries
+            .GroupBy(e => e.RiskLevel)
+            .ToDictionary(g => g.Key, g => g.ToList());
+
+        return Enum.GetValues<RiskLevel>()
+            .Select(level =>
+            {
+                var items = grouped.GetValueOrDefault(level, new List<SimplifiedPermissionEntry>());
+                var distinctUsers = items
+                    .SelectMany(e => e.UserLogins.Split(';', StringSplitOptions.RemoveEmptyEntries))
+                    .Select(u => u.Trim())
+                    .Where(u => u.Length > 0)
+                    .Distinct(StringComparer.OrdinalIgnoreCase)
+                    .Count();
+
+                return new PermissionSummary(
+                    Label: Labels[level],
+                    RiskLevel: level,
+                    Count: items.Count,
+                    DistinctUsers: distinctUsers);
+            })
+            .ToList();
+    }
+}