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/components/CodeEditor.vue

@@ -65,7 +65,6 @@ const langExtension = computed(() => {
 })
 
 const enhanceAutoCompletion = computed(() => {
-  console.log(props.language)
   return autocompletion({
     override: [enhanceCompletion(props.language), completeAnyWord],
   })