Complete GORM to sqlc migration

- Remove GORM dependency, use sqlc for type-safe SQL queries
- Update all handlers to use sqlc patterns (context, value types)
- Fix N+1 query problem in domain listing with JOIN query
- Enable SQL query logging in debug mode (USE_EMBEDDED=false)
- Add comprehensive comments for non-Go developers

backend/go.mod

@@ -4,11 +4,10 @@ go 1.25.0
 
 require (
 	github.com/gin-gonic/gin v1.10.0
+	github.com/go-sql-driver/mysql v1.9.3
 	github.com/golang-jwt/jwt/v5 v5.3.1
 	github.com/joho/godotenv v1.5.1
 	golang.org/x/crypto v0.49.0
-	gorm.io/driver/mysql v1.6.0
-	gorm.io/gorm v1.31.1
 )
 
 require (
@@ -22,10 +21,7 @@ require (
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/go-playground/validator/v10 v10.20.0 // indirect
-	github.com/go-sql-driver/mysql v1.9.3 // indirect
 	github.com/goccy/go-json v0.10.2 // indirect
-	github.com/jinzhu/inflection v1.0.0 // indirect
-	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect