[fix](fe) Skip auth for DeleteFromUsingCommand fallback in DeleteFromCommand

### What problem does this PR solve?

Problem Summary: Moving privChecked from StatementContext to CascadesContext
(for the CTE privilege bypass fix) caused a regression in DELETE commands
with complex WHERE clauses (e.g. NOT EXISTS subquery).

DeleteFromCommand sets skipAuth=true during initial Nereids planning because
DELETE does not need SELECT privilege. Previously, the privChecked flag on
StatementContext was shared across planners, so when DeleteFromUsingCommand
created a new planner, CheckPrivileges would see privChecked=true and skip.

After moving privChecked to CascadesContext, the new planner gets a fresh
CascadesContext with privChecked=false, causing CheckPrivileges to run
auth checks without skipAuth=true, failing on tables the user only has
LOAD privilege for.

Fix: Wrap both DeleteFromUsingCommand.run() call sites in skipAuth=true,
consistent with the initial planning phase's auth policy.

### Release note

None

### Check List (For Author)

- Test: Regression test (test_dml_delete_table_auth)
- Behavior changed: No
- Does this need documentation: No

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: seawinde

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/commands/DeleteFromCommand.java

@@ -207,8 +207,14 @@ public void run(ConnectContext ctx, StmtExecutor executor) throws Exception {
             }
         } catch (Exception e) {
             try {
-                new DeleteFromUsingCommand(nameParts, tableAlias, isTempPart, partitions,
-                        logicalQuery, Optional.empty(), false).run(ctx, executor);
+                // delete not need select priv, skip auth for the fallback planner
+                ctx.setSkipAuth(true);
+                try {
+                    new DeleteFromUsingCommand(nameParts, tableAlias, isTempPart, partitions,
+                            logicalQuery, Optional.empty(), false).run(ctx, executor);
+                } finally {
+                    ctx.setSkipAuth(originalIsSkipAuth);
+                }
                 return;
             } catch (Exception e2) {
                 LOG.warn("delete from command failed", e2);
@@ -219,8 +225,14 @@ public void run(ConnectContext ctx, StmtExecutor executor) throws Exception {
         // if table's enable_mow_light_delete is false, use `DeleteFromUsingCommand`
         if (olapTable.getKeysType() == KeysType.UNIQUE_KEYS && olapTable.getEnableUniqueKeyMergeOnWrite()
                 && !olapTable.getEnableMowLightDelete()) {
-            new DeleteFromUsingCommand(nameParts, tableAlias, isTempPart, partitions, logicalQuery,
-                    Optional.empty(), false).run(ctx, executor);
+            // delete not need select priv, skip auth for the fallback planner
+            ctx.setSkipAuth(true);
+            try {
+                new DeleteFromUsingCommand(nameParts, tableAlias, isTempPart, partitions, logicalQuery,
+                        Optional.empty(), false).run(ctx, executor);
+            } finally {
+                ctx.setSkipAuth(originalIsSkipAuth);
+            }
             return;
         }