fix(shared): filter due proposals by source_platform to prevent cross-platform race

Both Telegram and Discord deadline services were querying ALL due
proposals without filtering by source_platform. If the Telegram
service reached a Discord proposal first, it finalized the DB state
but skipped message handling. The Discord service then saw status
!= 'Voting' and never updated the Discord vote message.

Fix: GetDueProposalIdsAsync now accepts a sourcePlatform parameter
and filters at the DB level. Each service only processes its own
platform's proposals.

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

src/GmRelay.Bot/Features/Sessions/RescheduleSession/RescheduleVotingDeadlineService.cs

@@ -46,7 +46,7 @@ public sealed class RescheduleVotingDeadlineService(
     {
         try
         {
-            var proposalIds = await finalizer.GetDueProposalIdsAsync(ct);
+            var proposalIds = await finalizer.GetDueProposalIdsAsync("Telegram", ct);
 
             foreach (var proposalId in proposalIds)
             {

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

@@ -34,7 +34,7 @@ public sealed class DiscordRescheduleVotingDeadlineService(
     {
         try
         {
-            var proposalIds = await finalizer.GetDueProposalIdsAsync(ct);
+            var proposalIds = await finalizer.GetDueProposalIdsAsync("Discord", ct);
             foreach (var id in proposalIds)
             {
                 await TryFinalizeAsync(id, ct);

src/GmRelay.Shared/Features/Sessions/RescheduleSession/RescheduleVotingFinalizer.cs

@@ -26,7 +26,7 @@ public sealed class RescheduleVotingFinalizer(
     ISystemClock clock,
     ILogger<RescheduleVotingFinalizer> logger)
 {
-    public async Task<IReadOnlyList<Guid>> GetDueProposalIdsAsync(CancellationToken ct)
+    public async Task<IReadOnlyList<Guid>> GetDueProposalIdsAsync(string sourcePlatform, CancellationToken ct)
     {
         await using var connection = await dataSource.OpenConnectionAsync(ct);
         var proposalIds = (await connection.QueryAsync<Guid>(
@@ -36,10 +36,11 @@ public sealed class RescheduleVotingFinalizer(
             WHERE status = 'Voting'
               AND voting_deadline_at IS NOT NULL
               AND voting_deadline_at <= @Now
+              AND source_platform = @SourcePlatform
             ORDER BY voting_deadline_at
             LIMIT 25
             """,
-            new { Now = clock.UtcNow.UtcDateTime })).ToList();
+            new { Now = clock.UtcNow.UtcDateTime, SourcePlatform = sourcePlatform })).ToList();
 
         return proposalIds;
     }