feat: add support for SQL syntax highlighting

Add basic SQL syntax highlighting to `edit`.

Currently, `.sql` files are not detected as SQL and are opened without SQL syntax highlighting.

The highlighting should cover common SQL syntax such as:

- Keywords
- Comments
- Strings
- Numbers
- Boolean and `NULL` values
- Operators
- Common SQL functions

It would also be useful to support SQL code blocks in Markdown.

Start in edit's language-detection and syntax-highlighting paths, comparing the handling of existing languages. Check `.sql` file detection and SQL code blocks in Markdown. Done means common SQL keywords, comments, strings, numbers, booleans, NULL values, operators, and functions receive highlighting in both contexts.

Written by the indexing model from the issue text.