feat(missions): mission catalog + viewer mission repositories

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

SVSim.Database/Repositories/Mission/IViewerMissionRepository.cs

@@ -0,0 +1,34 @@
+using SVSim.Database.Models;
+
+namespace SVSim.Database.Repositories.Mission;
+
+public interface IViewerMissionRepository
+{
+    Task<List<ViewerMission>> GetMissionsAsync(long viewerId, CancellationToken ct);
+    Task<ViewerMission?> GetMissionByIdAsync(long viewerId, long missionId, CancellationToken ct);
+
+    Task<List<ViewerAchievement>> GetAchievementsAsync(long viewerId, CancellationToken ct);
+    Task<ViewerAchievement?> GetAchievementAsync(long viewerId, int achievementType, CancellationToken ct);
+
+    /// <summary>Reads counter rows for (viewerId, eventKey IN list, period IN list). Empty inputs return [].</summary>
+    Task<List<ViewerEventCounter>> GetCountersAsync(
+        long viewerId,
+        IReadOnlyCollection<string> eventKeys,
+        IReadOnlyCollection<string> periods,
+        CancellationToken ct);
+
+    /// <summary>Single-row counter read. Returns 0 if no row exists.</summary>
+    Task<int> GetCounterAsync(long viewerId, string eventKey, string period, CancellationToken ct);
+
+    /// <summary>Add a viewer mission row (in-memory; caller saves).</summary>
+    void AddMission(ViewerMission row);
+
+    /// <summary>Remove a viewer mission row (in-memory; caller saves).</summary>
+    void RemoveMission(ViewerMission row);
+
+    /// <summary>Add a viewer achievement row (in-memory; caller saves).</summary>
+    void AddAchievement(ViewerAchievement row);
+
+    /// <summary>Upsert a counter delta (in-memory; caller saves). Creates the row if missing.</summary>
+    Task UpsertCounterAsync(long viewerId, string eventKey, string period, int delta, CancellationToken ct);
+}