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/internal/api/handlers/aliases.go

@@ -1,7 +1,6 @@
 package handlers
 
 import (
-	"context"
 	"net/http"
 	"strconv"
 	"strings"