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/composables/sqlTable.ts

@@ -11,5 +11,6 @@ export function buildSqlScript(studentSql: string) {
   const table =
     sqlTables.find((item) => item.id === selectedTableId.value) ??
     sqlTables[0]
-  return `${table.setupSql}\n\n${studentSql}\n\nSELECT * FROM ${table.tableName};`
+  const normalizedSql = studentSql.trim().replace(/;?\s*$/, ";")
+  return `${table.setupSql}\n\n${normalizedSql}\n\nSELECT * FROM ${table.tableName};`
 }