fix: address SQL feature code review findings

- Normalize student SQL to end with exactly one semicolon before
  appending the trailing SELECT, so a missing trailing ; no longer
  produces a confusing parse error (sqlTable.ts)
- Remove unused description field from SqlTablePreset and all presets
  (dead data, nothing in the UI reads it)
- Clear output when the candidate table selection changes, so stale
  results from the previous table don't linger (SqlSection.vue)
- Remove stray console.log(props.language) debug statement
  (CodeEditor.vue)

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

src/data/sqlTables.ts

@@ -1,7 +1,6 @@
 export interface SqlTablePreset {
   id: string
   label: string
-  description: string
   tableName: string
   setupSql: string
 }
@@ -63,21 +62,18 @@ export const sqlTables: SqlTablePreset[] = [
   {
     id: "students",
     label: "学生成绩表",
-    description: "适合练习按分数筛选、批量更新、删除不及格记录",
     tableName: "students",
     setupSql: studentsSetupSql,
   },
   {
     id: "employees",
     label: "员工工资表",
-    description: "适合练习按部门分组调薪、按入职日期筛选",
     tableName: "employees",
     setupSql: employeesSetupSql,
   },
   {
     id: "products",
     label: "商品库存表",
-    description: "适合练习新增商品、调整库存、下架缺货商品",
     tableName: "products",
     setupSql: productsSetupSql,
   },