perf: completely avoid SELECT * in CreateProduct and UpdateProduct by selecting Category directly instead of First product load

feat: auto-generate unique SKU when blank during product creation to match Python FastAPI schema validation behavior

fix: normalize empty string SKU to nil/NULL to prevent unique key constraint violations on duplicate empty SKUs

perf: optimize Login GORM query with select-specific-columns, specific preloads, and remove the redundant First(company) query

perf: optimize DailyReport GORM query with select-specific-columns to avoid SELECT *

perf: optimize ListProducts, ListCategories, and ListOrders GORM queries with select-specific-columns and custom nested preload column selects

perf: completely fix N+1 query problem and select * in ListCompanies, ListBranches, and GetCurrentUser middleware

perf: optimize ListUsers and ListCompanies with database-level pagination and search

perf: optimize ListProducts using database-level pagination, search, and branch filtering

feat: add company_address to tenant registration request payload

fix: initialize empty slices instead of returning nil (null) to prevent frontend crashes

feat: migrate warungpos backend to Go with Tripay