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>

internal/util/reflect_test.go

@@ -8,7 +8,7 @@ import (
 	"testing"
 	"time"
 
-	"git.fsdpf.net/go/db/v2/internal/util"
+	"git.fsdpf.net/go/db/internal/util"
 	"github.com/stretchr/testify/suite"
 )