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>

engine/engine_config.go

@@ -1,11 +1,19 @@
 package engine
 
 import (
+	"database/sql"
 	"fmt"
 	"net/url"
 	"time"
+
+	"github.com/mattn/go-sqlite3"
 )
 
+type MockDBConfig struct {
+	Driver string
+	Mock   *sql.DB
+}
+
 // DBConfig 数据库配置结构体
 type DBConfig struct {
 	Driver          string
@@ -48,6 +56,7 @@ type DBConfig struct {
 		Synchronous int
 		Cache       string
 		BusyTimeout int
+		Raw         func(*sqlite3.SQLiteConn) error
 	}
 
 	SQLServer struct {
@@ -379,6 +388,16 @@ func WithSQLiteFile(file string) Option {
 	}
 }
 
+// SQLite 注册函数
+func WithSQLiteRaw(raw func(*sqlite3.SQLiteConn) error) Option {
+	return func(c *DBConfig) {
+		if c.Driver != "sqlite3" {
+			panic("WithSQLiteRegFn is only valid for sqlite3 driver")
+		}
+		c.SQLite.Raw = raw
+	}
+}
+
 func WithSQLiteJournal(journal string) Option {
 	return func(c *DBConfig) {
 		if c.Driver != "sqlite3" {