fix(discord): treat /newsession and /reschedule input as Moscow time (UTC+3)

DiscordNewSessionHandler.ParseTimeInput used DateTimeStyles.AssumeUniversal,
which interpreted user input as UTC. A user entering 15:00 got a session
scheduled at 18:00 MSK after rendering. Align with Telegram behavior by
treating input as Moscow time and converting to UTC before storage.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/GmRelay.DiscordBot/Features/Sessions/DiscordNewSessionHandler.cs

@@ -3,6 +3,7 @@ using GmRelay.DiscordBot.Infrastructure.Discord;
 using GmRelay.Shared.Domain;
 using GmRelay.Shared.Rendering;
 using Npgsql;
+using System.Globalization;
 
 namespace GmRelay.DiscordBot.Features.Sessions;
 
@@ -13,32 +14,38 @@ public sealed class DiscordNewSessionHandler(
     DiscordPermissionChecker permissionChecker,
     ILogger<DiscordNewSessionHandler> logger)
 {
+    private static readonly TimeSpan MoscowOffset = TimeSpan.FromHours(3);
+
     public static TimeParseResult ParseTimeInput(string input)
     {
-        if (DateTimeOffset.TryParseExact(
-            input.Trim(),
+        var trimmed = input.Trim();
+
+        if (DateTime.TryParseExact(
+            trimmed,
             "yyyy-MM-dd HH:mm",
-            System.Globalization.CultureInfo.InvariantCulture,
-            System.Globalization.DateTimeStyles.AssumeUniversal,
-            out var result))
+            CultureInfo.InvariantCulture,
+            DateTimeStyles.None,
+            out var dt1))
         {
-            if (result < DateTimeOffset.UtcNow)
+            var offset = new DateTimeOffset(dt1, MoscowOffset).ToUniversalTime();
+            if (offset < DateTimeOffset.UtcNow)
                 return new TimeParseResult(false, default, "Дата находится в прошлом.");
 
-            return new TimeParseResult(true, result.ToUniversalTime(), null);
+            return new TimeParseResult(true, offset, null);
         }
 
-        if (DateTimeOffset.TryParseExact(
-            input.Trim(),
+        if (DateTime.TryParseExact(
+            trimmed,
             "dd.MM.yyyy HH:mm",
-            System.Globalization.CultureInfo.InvariantCulture,
-            System.Globalization.DateTimeStyles.AssumeUniversal,
-            out var altResult))
+            CultureInfo.InvariantCulture,
+            DateTimeStyles.None,
+            out var dt2))
         {
-            if (altResult < DateTimeOffset.UtcNow)
+            var offset = new DateTimeOffset(dt2, MoscowOffset).ToUniversalTime();
+            if (offset < DateTimeOffset.UtcNow)
                 return new TimeParseResult(false, default, "Дата находится в прошлом.");
 
-            return new TimeParseResult(true, altResult.ToUniversalTime(), null);
+            return new TimeParseResult(true, offset, null);
         }
 
         return new TimeParseResult(false, default, "Некорректный формат даты. Используйте YYYY-MM-DD HH:mm или DD.MM.YYYY HH:mm");

tests/GmRelay.Bot.Tests/Discord/DiscordNewSessionHandlerTests.cs

@@ -17,6 +17,17 @@ public sealed class DiscordNewSessionHandlerTests
 
     // --- Runtime tests for ParseTimeInput (static, no DB) ---
 
+    [Fact]
+    public void ParseTimeInput_ShouldTreatInputAsMoscowTime()
+    {
+        var result = DiscordNewSessionHandler.ParseTimeInput("2026-06-01 15:00");
+        Assert.True(result.IsSuccess);
+        // 15:00 MSK = 12:00 UTC
+        Assert.Equal(12, result.Value.Hour);
+        Assert.Equal(0, result.Value.Minute);
+        Assert.Equal(TimeSpan.Zero, result.Value.Offset);
+    }
+
     [Fact]
     public void ParseTimeInput_ShouldParseDiscordDateFormat()
     {
@@ -28,7 +39,8 @@ public sealed class DiscordNewSessionHandlerTests
         Assert.Equal(expected.Year, result.Value.Year);
         Assert.Equal(expected.Month, result.Value.Month);
         Assert.Equal(expected.Day, result.Value.Day);
-        Assert.Equal(19, result.Value.Hour);
+        // Input is treated as Moscow time; 19:30 MSK = 16:30 UTC
+        Assert.Equal(16, result.Value.Hour);
         Assert.Equal(30, result.Value.Minute);
     }