feat(platform): feature flags + user settings foundation (#35)

src/InboxIntel.Domain/Entities/FeatureFlag.cs

@@ -0,0 +1,42 @@
+using InboxIntel.Domain.Common;
+
+namespace InboxIntel.Domain.Entities;
+
+/// <summary>
+/// System-wide feature flag (docs/discovery/multi-provider/04). The admin master switches:
+/// a disabled flag turns its feature off for EVERYONE regardless of user preferences.
+/// Reads are fail-closed — an unknown key counts as disabled.
+/// </summary>
+public class FeatureFlag : AuditableEntity
+{
+    /// <summary>Stable key, e.g. "ai.enabled", "provider.google".</summary>
+    public string Key { get; set; } = string.Empty;
+
+    public bool Enabled { get; set; }
+
+    /// <summary>True = a user preference may turn the feature OFF for themselves
+    /// (never on beyond the flag); false = system-only switch.</summary>
+    public bool UserOverridable { get; set; }
+
+    public string? Description { get; set; }
+}
+
+/// <summary>
+/// Per-user preferences (docs/discovery/multi-provider/04). One row per user, created
+/// lazily; absent row = defaults. AiOptIn defaults true so enabling the ai.enabled flag
+/// behaves exactly like today until a user opts out.
+/// </summary>
+public class UserSetting : AuditableEntity
+{
+    public Guid UserId { get; set; }
+    public User? User { get; set; }
+
+    /// <summary>"system" | "light" | "dark".</summary>
+    public string Theme { get; set; } = "dark";
+
+    /// <summary>Master per-user AI opt-in (effective only while ai.enabled is on).</summary>
+    public bool AiOptIn { get; set; } = true;
+
+    /// <summary>Free-form UI preferences (layout, density, notifications) as JSON.</summary>
+    public string? PreferencesJson { get; set; }
+}