feat(ui): 🎨 Implement schema and table management screens

* Add schema management screen with list and editor
* Implement table management screen with list and editor
* Create data operations for schema and table management
* Define UI rules and guidelines for consistency
* Ensure circular tab navigation and keyboard shortcuts
* Add forms for creating and editing schemas and tables
* Implement confirmation dialogs for destructive actions

pkg/ui/main_menu.go

@@ -0,0 +1,62 @@
+package ui
+
+import (
+	"fmt"
+
+	"github.com/gdamore/tcell/v2"
+	"github.com/rivo/tview"
+)
+
+// createMainMenu creates the main menu screen
+func (se *SchemaEditor) createMainMenu() tview.Primitive {
+	flex := tview.NewFlex().SetDirection(tview.FlexRow)
+
+	// Title with database name
+	dbName := se.db.Name
+	if dbName == "" {
+		dbName = "Untitled"
+	}
+	updateAtStr := ""
+	if se.db.UpdatedAt != "" {
+		updateAtStr = fmt.Sprintf("Updated @ %s", se.db.UpdatedAt)
+	}
+	titleText := fmt.Sprintf("[::b]RelSpec Schema Editor\n[::d]Database: %s %s\n[::d]Press arrow keys to navigate, Enter to select", dbName, updateAtStr)
+	title := tview.NewTextView().
+		SetText(titleText).
+		SetDynamicColors(true)
+
+	// Menu options
+	menu := tview.NewList().
+		AddItem("Edit Database", "Edit database name, description, and properties", 'e', func() {
+			se.showEditDatabaseForm()
+		}).
+		AddItem("Manage Schemas", "View, create, edit, and delete schemas", 's', func() {
+			se.showSchemaList()
+		}).
+		AddItem("Manage Tables", "View and manage tables in schemas", 't', func() {
+			se.showTableList()
+		}).
+		AddItem("Manage Domains", "View, create, edit, and delete domains", 'd', func() {
+			se.showDomainList()
+		}).
+		AddItem("Save Database", "Save database to file or database", 'w', func() {
+			se.showSaveScreen()
+		}).
+		AddItem("Exit Editor", "Exit the editor", 'q', func() {
+			se.app.Stop()
+		})
+
+	menu.SetBorder(true).SetTitle(" Menu ").SetTitleAlign(tview.AlignLeft)
+	menu.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey {
+		if event.Key() == tcell.KeyEscape {
+			se.showExitEditorConfirm()
+			return nil
+		}
+		return event
+	})
+
+	flex.AddItem(title, 5, 0, false).
+		AddItem(menu, 0, 1, true)
+
+	return flex
+}