docs: Add CLAUDE.md with codebase guidance

Create comprehensive documentation for future Claude Code instances working in this repository, including:
- Development commands for testing, building, and code quality
- Core architecture overview of the SQL query builder system
- Directory structure and component explanations
- Testing patterns and conventions
- Key dependencies and their purposes

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

Co-Authored-By: Claude <noreply@anthropic.com>

exp/select_clauses.go

@@ -22,6 +22,7 @@ type (
 
 		Joins() JoinExpressions
 		JoinsAppend(jc JoinExpression) SelectClauses
+		JoinsPrepend(jc JoinExpression) SelectClauses
 
 		Where() ExpressionList
 		ClearWhere() SelectClauses
@@ -41,6 +42,7 @@ type (
 		GroupBy() ColumnListExpression
 		SetGroupBy(cl ColumnListExpression) SelectClauses
 		GroupByAppend(cl ColumnListExpression) SelectClauses
+		ClearGroupBy() SelectClauses
 
 		Limit() interface{}
 		HasLimit() bool
@@ -197,6 +199,12 @@ func (c *selectClauses) JoinsAppend(jc JoinExpression) SelectClauses {
 	return ret
 }
 
+func (c *selectClauses) JoinsPrepend(jc JoinExpression) SelectClauses {
+	ret := c.clone()
+	ret.joins = append(JoinExpressions{jc}, ret.joins...)
+	return ret
+}
+
 func (c *selectClauses) Where() ExpressionList {
 	return c.where
 }
@@ -310,6 +318,12 @@ func (c *selectClauses) SetGroupBy(cl ColumnListExpression) SelectClauses {
 	return ret
 }
 
+func (c *selectClauses) ClearGroupBy() SelectClauses {
+	ret := c.clone()
+	ret.groupBy = nil
+	return ret
+}
+
 func (c *selectClauses) Limit() interface{} {
 	return c.limit
 }