refactor: restructure in entirety

internal/models/models.go

@@ -0,0 +1,46 @@
+package models
+
+// Product represents a product in the database
+type Product struct {
+	SKU            string  `json:"sku"`
+	Name           string  `json:"name"`
+	HSNCode        string  `json:"hsn_code"`
+	BasePrice      float64 `json:"base_price"`
+	WholesalePrice float64 `json:"wholesale_price"`
+	GSTRate        float64 `json:"gst_rate"`
+	SmallOrderQty  int     `json:"small_order_qty"`
+	SmallOrderFee  float64 `json:"small_order_fee"` // Convenience fee for orders below SmallOrderQty
+	Unit           string  `json:"unit"`            // Unit of measurement (e.g., "pcs", "kg", "box")
+	UserID         string  `json:"user_id"`
+	CreatedAt      string  `json:"created_at"`
+}
+
+// Invoice represents a stored invoice
+type Invoice struct {
+	ID              string `json:"id"`                // UUID
+	HumanReadableID string `json:"human_readable_id"` // Formatted ID like INV/12-2025/001
+	Data            string `json:"data"`              // JSON blob of invoice details
+	UserID          string `json:"user_id"`
+	CreatedAt       string `json:"created_at"`
+}
+
+// User represents an authenticated user
+type User struct {
+	ID             string `json:"id"`
+	Email          string `json:"email"`
+	Password       string `json:"-"`
+	CompanyDetails string `json:"company_details"` // Multiline company details for invoice header
+	BankDetails    string `json:"bank_details"`    // Multiline bank details for invoice footer
+	InvoicePrefix  string `json:"invoice_prefix"`  // Prefix for invoice IDs (e.g., INV, BILL)
+	InvoiceCounter int    `json:"invoice_counter"` // Auto-incrementing counter for invoice serial numbers
+	CreatedAt      string `json:"created_at"`
+}
+
+// BuyerDetails represents a buyer/customer for invoices
+type BuyerDetails struct {
+	ID        string `json:"id"`
+	UserID    string `json:"user_id"`
+	Name      string `json:"name"`    // Display name for selection
+	Details   string `json:"details"` // Multiline buyer details
+	CreatedAt string `json:"created_at"`
+}