Finalize API envelopes and close validation drift tasks

Contracts/Responses.cs

@@ -54,3 +54,28 @@ public record ResultItemDto(
     IReadOnlyList<int> LinkedIds,
     IReadOnlyList<string> LinkedTitles
 );
+
+public record AuthSessionResponse(Guid Id, string Username, string? DisplayName, bool IsAdmin);
+
+public record StateSummaryResponse(
+    Phase CurrentPhase,
+    bool VotesFinal,
+    bool HasJoker,
+    bool ResultsOpen,
+    DateTimeOffset UpdatedAt,
+    int Players,
+    int Suggestions,
+    int Votes
+);
+
+public record MeResponse(
+    Guid Id,
+    string Username,
+    string? DisplayName,
+    bool IsAdmin,
+    Phase CurrentPhase,
+    bool VotesFinal,
+    bool HasJoker
+);
+
+public record PhaseTransitionResponse(Phase CurrentPhase, bool ResultsOpen);