fix: Set from_source in ExpressionLifter to fix QUALIFY regression

Fixes the QUALIFY clause regression introduced by the from_source migration.
The issue was that ExpressionLifter was only setting the deprecated from_table
field when creating CTEs, not the new from_source field. This caused the query
engine to not properly recognize CTE references.

Changes:
- Updated ExpressionLifter to set both from_source (preferred) and from_table (deprecated)
- Added logic in StatementExecutor to re-extract base table when preprocessing adds CTEs
- All 28 formal tests now passing (including qualify.sql)
- All 396 Rust unit tests passing

The ExpressionLifter creates CTEs like:
  WITH __lifted_1 AS (SELECT *, ROW_NUMBER() ... AS rn FROM sales)
  SELECT ... FROM __lifted_1

Now from_source is properly set to TableSource::Table("__lifted_1") so the
query engine can find the CTE in the cte_context and use it as the source table.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: TimelordUK

src/execution/statement_executor.rs

@@ -154,9 +154,22 @@ impl StatementExecutor {
         stats.preprocessing_time_ms = preprocess_start.elapsed().as_secs_f64() * 1000.0;
         stats.preprocessing_applied = preprocessing_applied;
 
+        // Step 2.5: Re-check source table if preprocessing added CTEs
+        // If the transformed statement has CTEs (e.g., from ExpressionLifter),
+        // we need to use the source table that was passed in, not the extracted base table,
+        // because the CTE itself becomes the data source.
+        let final_source_table = if !transformed_stmt.ctes.is_empty() {
+            // Has CTEs - need to extract base table from the actual CTE definitions
+            // to get the underlying data source
+            Self::extract_base_table(&transformed_stmt, context)
+        } else {
+            source_table
+        };
+
         // Step 3: Execute the transformed statement directly via QueryEngine
         let exec_start = Instant::now();
-        let result_view = self.execute_ast(transformed_stmt.clone(), source_table, context)?;
+        let result_view =
+            self.execute_ast(transformed_stmt.clone(), final_source_table, context)?;
         stats.execution_time_ms = exec_start.elapsed().as_secs_f64() * 1000.0;
 
         // Step 4: If this was a SELECT INTO statement, store the result as a temp table

src/query_plan/expression_lifter.rs

@@ -354,8 +354,16 @@ impl ExpressionLifter {
         }
 
         stmt.select_items = new_select_items;
-        stmt.from_table = Some(cte_name.clone());
-        stmt.from_subquery = None;
+        // Set from_source to reference the CTE (preferred)
+        stmt.from_source = Some(crate::sql::parser::ast::TableSource::Table(
+            cte_name.clone(),
+        ));
+        // Also set deprecated field for backward compatibility
+        #[allow(deprecated)]
+        {
+            stmt.from_table = Some(cte_name.clone());
+            stmt.from_subquery = None;
+        }
         stmt.where_clause = None; // Already in the CTE
 
         CTE {