Clarify baseConnectionString in connection string builder example

[Copilot]

The Connection string builder section showed a code snippet using baseConnectionString, but its definition was outside the snippet region and invisible to readers, causing a confusing ArgumentException when users passed a bare file path instead of a valid connection string.

Changes

• docs/standard/data/sqlite/connection-strings.md: Added a [!NOTE] callout before the code snippet clarifying that baseConnectionString is an existing connection string, such as Data Source=EncryptionSample.db.

• Fixes Connection string builder code error #39682

---

Internal previews

📄 File	🔗 Preview link
docs/standard/data/sqlite/connection-strings.md	docs/standard/data/sqlite/connection-strings

[Copilot]

Copilot was unable to review this pull request because there is no eligible user to bill. To allow Copilot reviews on bot-authored pull requests, enable direct organization billing in your organization's Copilot settings.