feat(mission): /mission/buy_additional_right stub (refresh-only, no decomp)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Controllers/MissionController.cs

@@ -116,6 +116,23 @@ public class MissionController : SVSimController
         return Ok(dto);
     }
 
+    [HttpPost("buy_additional_right")]
+    public async Task<IActionResult> BuyAdditionalRight(BaseRequest _, CancellationToken ct)
+    {
+        if (!TryGetViewerId(out long viewerId)) return Unauthorized();
+
+        // The client-side task class is absent from the decompilation; the URL is
+        // registered but no Parse() is documented. Spec marks the shape as INFERRED.
+        // Safe stub: refresh MissionInfoDetail and let the client re-render — same
+        // shape as /mission/info. No currency debit until we see a real wire call.
+        var viewer = await LoadViewer(viewerId, ct);
+        await _state.EnsureCurrentAsync(viewer.Id, ct);
+        await _db.SaveChangesAsync(ct);
+
+        var dto = await _assembler.BuildAsync(viewer, ct);
+        return Ok(dto);
+    }
+
     private Task<Viewer> LoadViewer(long viewerId, CancellationToken ct) =>
         _db.Viewers
             .Include(v => v.MissionData)