feat: structure candidate SQL table data as columns/rows

- Replace literal setupSql strings with structured columns/rows model
- Add SqlColumn interface and updated SqlTablePreset with columns/rows arrays
- Implement toSqlLiteral() for value escaping and buildSetupSql() for SQL generation
- Update sqlTable.ts to call buildSetupSql() instead of accessing setupSql field
- Maintains data parity with existing tables (students, employees, products)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/composables/sqlTable.ts

@@ -1,5 +1,5 @@
 import { ref } from "vue"
-import { defaultSqlTableId, sqlTables } from "../data/sqlTables"
+import { buildSetupSql, defaultSqlTableId, sqlTables } from "../data/sqlTables"
 
 export const selectedTableId = ref(defaultSqlTableId)
 
@@ -12,5 +12,5 @@ export function buildSqlScript(studentSql: string) {
     sqlTables.find((item) => item.id === selectedTableId.value) ??
     sqlTables[0]
   const normalizedSql = studentSql.trim().replace(/;?\s*$/, ";")
-  return `${table.setupSql}\n\n${normalizedSql}\n\nSELECT * FROM ${table.tableName};`
+  return `${buildSetupSql(table)}\n\n${normalizedSql}\n\nSELECT * FROM ${table.tableName};`
 }