FRE-683: Add contacts & attachments management

- Implemented contact CRUD operations (list, add, edit, delete)
- Implemented attachment management (list, upload, download)
- Created internal/contact/manager.go for contact persistence
- Created internal/attachment/manager.go for attachment storage
- Added CLI commands in cmd/contacts.go and cmd/attachments.go
- Integrated contact and attachment commands into root CLI

Files:
- internal/contact/types.go - Contact data models
- internal/contact/manager.go - Contact CRUD operations
- internal/attachment/manager.go - Attachment file operations
- cmd/contacts.go - Contact CLI commands
- cmd/attachments.go - Attachment CLI commands

Contacts stored in ~/.config/pop/contacts.json
Attachments stored in ~/.config/pop/attachments/

cmd/contacts.go

@@ -0,0 +1,174 @@
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/frenocorp/pop/internal/contact"
+	"github.com/spf13/cobra"
+)
+
+func contactCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "contact",
+		Short: "Manage contacts",
+		Long:  `List, add, edit, and delete contacts.`,
+	}
+
+	cmd.AddCommand(contactListCmd())
+	cmd.AddCommand(contactAddCmd())
+	cmd.AddCommand(contactEditCmd())
+	cmd.AddCommand(contactDeleteCmd())
+
+	return cmd
+}
+
+func contactListCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "list",
+		Short: "List all contacts",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			manager := contact.NewContactManager()
+			
+			page, _ := cmd.Flags().GetInt("page")
+			pageSize, _ := cmd.Flags().GetInt("page-size")
+			search, _ := cmd.Flags().GetString("search")
+			
+			req := contact.ListContactsRequest{
+				Page:   page,
+				PageSize: pageSize,
+				Search: search,
+			}
+			
+			resp, err := manager.List(req)
+			if err != nil {
+				return fmt.Errorf("failed to list contacts: %w", err)
+			}
+			
+			if len(resp.Contacts) == 0 {
+				fmt.Println("No contacts found")
+				return nil
+			}
+			
+			data, _ := json.MarshalIndent(resp.Contacts, "", "  ")
+			fmt.Println(string(data))
+			return nil
+		},
+	}
+
+	cmd.Flags().IntP("page", "p", 0, "Page number")
+	cmd.Flags().IntP("page-size", "n", 10, "Items per page")
+	cmd.Flags().StringP("search", "s", "", "Search by email or name")
+
+	return cmd
+}
+
+func contactAddCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "add",
+		Short: "Add a new contact",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			email, _ := cmd.Flags().GetString("email")
+			name, _ := cmd.Flags().GetString("name")
+			phone, _ := cmd.Flags().GetString("phone")
+			
+			if email == "" {
+				return fmt.Errorf("email is required")
+			}
+			
+			manager := contact.NewContactManager()
+			req := contact.CreateContactRequest{
+				Email:  email,
+				Name:   name,
+				Phone:  phone,
+			}
+			
+			contact, err := manager.Create(req)
+			if err != nil {
+				return fmt.Errorf("failed to create contact: %w", err)
+			}
+			
+			data, _ := json.MarshalIndent(contact, "", "  ")
+			fmt.Printf("Created contact:\n%s\n", string(data))
+			return nil
+		},
+	}
+
+	cmd.Flags().StringP("email", "e", "", "Contact email (required)")
+	cmd.Flags().StringP("name", "n", "", "Contact name")
+	cmd.Flags().StringP("phone", "p", "", "Contact phone")
+
+	return cmd
+}
+
+func contactEditCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "edit <id>",
+		Short: "Edit a contact",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if len(args) < 1 {
+				return fmt.Errorf("contact ID is required")
+			}
+			
+			id := args[0]
+			manager := contact.NewContactManager()
+			
+			_, err := manager.Get(id)
+			if err != nil {
+				return fmt.Errorf("failed to get contact: %w", err)
+			}
+			
+			name, _ := cmd.Flags().GetString("name")
+			phone, _ := cmd.Flags().GetString("phone")
+			address, _ := cmd.Flags().GetString("address")
+			notes, _ := cmd.Flags().GetString("notes")
+			
+			req := contact.UpdateContactRequest{
+				Name:   &name,
+				Phone:  &phone,
+				Address: &address,
+				Notes:  &notes,
+			}
+			
+			updated, err := manager.Update(id, req)
+			if err != nil {
+				return fmt.Errorf("failed to update contact: %w", err)
+			}
+			
+			data, _ := json.MarshalIndent(updated, "", "  ")
+			fmt.Printf("Updated contact:\n%s\n", string(data))
+			return nil
+		},
+	}
+
+	cmd.Flags().StringP("name", "n", "", "New name")
+	cmd.Flags().StringP("phone", "p", "", "New phone")
+	cmd.Flags().StringP("address", "a", "", "New address")
+	cmd.Flags().StringP("notes", "o", "", "New notes")
+
+	return cmd
+}
+
+func contactDeleteCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "delete <id>",
+		Short: "Delete a contact",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if len(args) < 1 {
+				return fmt.Errorf("contact ID is required")
+			}
+			
+			id := args[0]
+			manager := contact.NewContactManager()
+			
+			if err := manager.Delete(id); err != nil {
+				return fmt.Errorf("failed to delete contact: %w", err)
+			}
+			
+			fmt.Printf("Deleted contact: %s\n", id)
+			return nil
+		},
+	}
+
+	return cmd
+}