ui(dialogs): make destructive query and DML preview dialogs adaptive and prevent table name overflow #1642

Problem

1. Non-adaptive dialog constraints:
   In lib/features/workspace/destructive_query_dialog.dart, the dialog card uses hardcoded fixed constraints:

   constraints: const material.BoxConstraints(
     minWidth: 540,
     maxWidth: 680,
     minHeight: 440,
     maxHeight: 580,
   ),
   child: material.FocusTraversalGroup(
     child: material.SizedBox(height: 540, ...),

   It does not use WindowLayout.dialogConstraints(context) or WindowLayout.dialogSymmetricInsets(context). When running on compact window widths (e.g. 520px) or with a UI scale of 1.25x+, the dialog overflows screen bounds.

2. Unconstrained table name in DML Preview:
   In lib/features/workspace/dml_preview_dialog.dart, the header row displays Text('${widget.plan.schema}.${widget.plan.tableName}') without Flexible and without overflow: TextOverflow.ellipsis. For long table names, it causes horizontal RenderFlex overflow.

Change

• Migrate destructive_query_dialog.dart to use WindowLayout.dialogConstraints(context) and WindowLayout.dialogSymmetricInsets(context).
• Wrap the table name in dml_preview_dialog.dart with Flexible(child: Text(..., overflow: TextOverflow.ellipsis)).