Skip running jobs collector when login lacks msdb access

[erikdarlingdata]

Closes #656

Summary

• Add HAS_DBACCESS('msdb') check to the connectivity probe so we detect msdb permissions at connect time
• Gate the running_jobs collector via IsCollectorSupported() — collector is silently skipped instead of failing
• Show a yellow warning message on the Running Jobs tab: "Running Jobs requires msdb access. Grant the login access to msdb to enable this feature."

Changes

• ServerConnectionStatus.HasMsdbAccess — new property, defaults to true
• ServerManager.cs — connectivity probe query adds HAS_DBACCESS(N'msdb') column
• RemoteCollectorService.cs — IsCollectorSupported() gates running_jobs on hasMsdbAccess
• ServerTab.xaml / .cs — warning TextBlock, collapsed by default, shown when !hasMsdbAccess
• MainWindow.xaml.cs — passes status.HasMsdbAccess to ServerTab constructor

Test plan

• Connect with sa login — Running Jobs tab works normally, no warning
• Connect with a login that lacks msdb access — warning shown, no collector errors in log
• Azure SQL DB / AWS RDS — existing gates still skip running_jobs before msdb check

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