fix(expander): use valid MySQL syntax for edge case tests

MySQL doesn't support unqualified `*` mixed with other columns (e.g.,
`SELECT *, *` or `SELECT id, *, name`). These are valid PostgreSQL
but invalid MySQL syntax.

Update MySQL tests to use table-qualified stars which are valid:
- `SELECT authors.*, authors.*` instead of `SELECT *, *`
- `SELECT id, authors.*, name` instead of `SELECT id, *, name`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: kyleconroy

internal/x/expander/expander_test.go

@@ -270,6 +270,16 @@ func TestExpandMySQL(t *testing.T) {
 			query:    "SELECT authors.* FROM authors",
 			expected: "SELECT authors.id,authors.name,authors.bio FROM authors;",
 		},
+		{
+			name:     "double table qualified star",
+			query:    "SELECT authors.*, authors.* FROM authors",
+			expected: "SELECT authors.id,authors.name,authors.bio,authors.id,authors.name,authors.bio FROM authors;",
+		},
+		{
+			name:     "star in middle of columns table qualified",
+			query:    "SELECT id, authors.*, name FROM authors",
+			expected: "SELECT id,authors.id,authors.name,authors.bio,name FROM authors;",
+		},
 		{
 			name:     "count star not expanded",
 			query:    "SELECT COUNT(*) FROM authors",
@@ -280,9 +290,6 @@ func TestExpandMySQL(t *testing.T) {
 			query:    "SELECT COUNT(*), name FROM authors GROUP BY name",
 			expected: "SELECT COUNT(*), name FROM authors GROUP BY name", // No change
 		},
-		// Note: "double star" and "star in middle of columns" tests are skipped for MySQL
-		// because the intermediate query formatting produces invalid MySQL syntax.
-		// These are edge cases that rarely occur in real-world usage.
 	}
 
 	for _, tc := range tests {