feat(web): dashboard session deletion and E2E coverage for issue #150

- Add DeleteSessionAsync to ISessionStore/SessionService (unpublish portfolio card,
  remove bot-created empty forum topic, update batch message).
- Add DeleteSessionForCurrentUserAsync to AuthorizedSessionService with audit log.
- Add delete button + confirmation dialog to GroupDetails.razor.
- Extend dashboard Playwright tests with edit persistence and delete verification.
- Update AuthorizedSessionServiceTests with delete authorization coverage.
- Mark issue #150 as done in tests/e2e/README.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/e2e/runner/TelegramUserClient.cs

@@ -17,6 +17,8 @@ public sealed class TelegramUserClient : IDisposable
         _client = new Client(_ => Environment.GetEnvironmentVariable(_));
     }
 
+    public long CurrentUserId => _client.UserId;
+
     public async Task ConnectAsync(CancellationToken cancellationToken = default)
     {
         var me = await _client.LoginUserIfNeeded();