refactor: завершить platform migration и удалить deprecated telegram_* scaffolding

- Добавлены миграции V024 (backfill + deprecation comments + calendar_subscriptions platform identity) и V025 (backfill proposed_by_external_user_id)
- Все Bot handlers переведены с telegram_id/chat_id на platform + external_*
- Shared handlers очищены от COALESCE fallback с telegram_* колонками
- DiscordBot очищен от COALESCE fallback
- Web SessionService и CalendarSubscriptionService переведены на external_*
- HandleRsvpHandler: убран legacy UNION с gm_telegram_id, теперь только group_managers
- RescheduleVotingFinalizer: переведен на external_username/external_user_id
- Tests: добавлены asserts для V024/V025
- Версия обновлена до 3.1.0

Bump version → 3.1.0

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

src/GmRelay.Shared/Features/Confirmation/HandleRsvp/HandleRsvpHandler.cs

@@ -56,8 +56,8 @@ public sealed class HandleRsvpHandler(
                 FROM session_participants sp
                 JOIN players p ON p.id = sp.player_id
                 WHERE sp.session_id = @SessionId
-                  AND COALESCE(p.platform, 'Telegram') = @Platform
-                  AND COALESCE(p.external_user_id, p.telegram_id::TEXT) = @ExternalUserId
+                  AND p.platform = @Platform
+                  AND p.external_user_id = @ExternalUserId
                   AND sp.is_gm = false
                   AND sp.registration_status = @Active
             )
@@ -90,8 +90,8 @@ public sealed class HandleRsvpHandler(
               AND  player_id = (
                     SELECT id
                     FROM players
-                    WHERE COALESCE(platform, 'Telegram') = @Platform
-                      AND COALESCE(external_user_id, telegram_id::TEXT) = @ExternalUserId
+                    WHERE platform = @Platform
+                      AND external_user_id = @ExternalUserId
                     LIMIT 1
               )
               AND  registration_status = @Active
@@ -265,10 +265,10 @@ public sealed class HandleRsvpHandler(
 
             var participants = (await connection.QueryAsync<ParticipantRsvpRow>(
                 """
-                SELECT COALESCE(p.platform, 'Telegram') AS Platform,
-                       COALESCE(p.external_user_id, p.telegram_id::TEXT) AS ExternalUserId,
+                SELECT p.platform AS Platform,
+                       p.external_user_id AS ExternalUserId,
                        p.display_name AS DisplayName,
-                       COALESCE(p.external_username, p.telegram_username) AS ExternalUsername,
+                       p.external_username AS ExternalUsername,
                        sp.rsvp_status AS RsvpStatus,
                        sp.registration_status AS RegistrationStatus,
                        sp.is_gm AS IsGm
@@ -312,23 +312,13 @@ public sealed class HandleRsvpHandler(
         var rows = await connection.QueryAsync<RsvpRecipientRow>(
             """
             SELECT DISTINCT
-                   COALESCE(p.platform, 'Telegram') AS Platform,
-                   COALESCE(p.external_user_id, p.telegram_id::TEXT) AS ExternalUserId,
+                   p.platform AS Platform,
+                   p.external_user_id AS ExternalUserId,
                    p.display_name AS DisplayName,
-                   COALESCE(p.external_username, p.telegram_username) AS ExternalUsername
+                   p.external_username AS ExternalUsername
             FROM group_managers gm
             JOIN players p ON p.id = gm.player_id
             WHERE gm.group_id = @GroupId
-            UNION
-            SELECT DISTINCT
-                   COALESCE(p.platform, 'Telegram') AS Platform,
-                   COALESCE(p.external_user_id, p.telegram_id::TEXT) AS ExternalUserId,
-                   p.display_name AS DisplayName,
-                   COALESCE(p.external_username, p.telegram_username) AS ExternalUsername
-            FROM game_groups g
-            JOIN players p ON p.telegram_id = g.gm_telegram_id
-            WHERE g.id = @GroupId
-              AND g.gm_telegram_id IS NOT NULL
             """,
             new { GroupId = groupId },
             transaction);

src/GmRelay.Shared/Features/Confirmation/SendConfirmation/SendConfirmationHandler.cs

@@ -45,10 +45,10 @@ public sealed class SendConfirmationHandler(
                    s.title,
                    s.scheduled_at AS ScheduledAt,
                    s.group_id AS GroupId,
-                   COALESCE(g.platform, 'Telegram') AS Platform,
-                   COALESCE(g.external_group_id, g.telegram_chat_id::TEXT) AS ExternalGroupId,
+                   g.platform AS Platform,
+                   g.external_group_id AS ExternalGroupId,
                    g.name AS DisplayName,
-                   COALESCE(g.external_channel_id, g.telegram_chat_id::TEXT) AS ExternalChannelId,
+                   g.external_channel_id AS ExternalChannelId,
                    s.thread_id AS ThreadId,
                    s.notification_mode AS NotificationMode
             FROM sessions s
@@ -65,10 +65,10 @@ public sealed class SendConfirmationHandler(
 
         var participants = (await connection.QueryAsync<ConfirmationParticipantRow>(
             """
-            SELECT COALESCE(p.platform, 'Telegram') AS Platform,
-                   COALESCE(p.external_user_id, p.telegram_id::TEXT) AS ExternalUserId,
+            SELECT p.platform AS Platform,
+                   p.external_user_id AS ExternalUserId,
                    p.display_name AS DisplayName,
-                   COALESCE(p.external_username, p.telegram_username) AS ExternalUsername,
+                   p.external_username AS ExternalUsername,
                    sp.rsvp_status AS RsvpStatus,
                    sp.registration_status AS RegistrationStatus,
                    sp.is_gm AS IsGm