feat(ui): make SQL toggle retroactive for entire session

The SQL toggle (`ctrl+s`) now shows/hides SQL for all queries in the
current session, not just future queries.

Changes:
- Always store SQL in message history (regardless of ShowSQL state)
- Filter SQL messages during rendering based on current ShowSQL value
- Refresh viewport immediately when toggling so change is visible

Now when you toggle SQL on, all previously executed queries in the
session will show their SQL. Toggle it off and they all hide again.

Closes #163

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: cpcloud

internal/app/chat.go

@@ -710,12 +710,11 @@ func (m *Model) handleSQLResult(msg sqlResultMsg) tea.Cmd {
 		return m.startFallbackStream(msg.Question)
 	}
 
-	// Show the generated SQL if the user has opted in via /sql.
-	if m.chat.ShowSQL {
-		m.chat.Messages = append(m.chat.Messages, chatMessage{
-			Role: "sql", Content: msg.SQL,
-		})
-	}
+	// Always store the SQL in the message history so we can retroactively
+	// show/hide it when the user toggles SQL display.
+	m.chat.Messages = append(m.chat.Messages, chatMessage{
+		Role: "sql", Content: msg.SQL,
+	})
 
 	// Stage 2: summarize results via streaming LLM call.
 	resultsTable := llm.FormatResultsTable(msg.Columns, msg.Rows)
@@ -824,6 +823,8 @@ func (m *Model) toggleSQL() {
 		return
 	}
 	m.chat.ShowSQL = !m.chat.ShowSQL
+	// Refresh viewport to immediately show/hide SQL for all messages.
+	m.refreshChatViewport()
 }
 
 // sqlHintItem renders the ctrl+s hint with color indicating whether SQL
@@ -993,6 +994,10 @@ func (m *Model) renderChatMessages() string {
 				rendered += "\n" + lipgloss.NewStyle().Foreground(textDim).Render(sep)
 			}
 		case "sql":
+			// Only render SQL messages when ShowSQL is true.
+			if !m.chat.ShowSQL {
+				continue
+			}
 			// Leave room for glamour's code block padding/border.
 			sqlWidth := innerW - 8
 			if sqlWidth < 30 {