fix(tui): enable Ctrl+C/ESC to cancel running backup/restore operations

PROBLEM: Users could not interrupt backup or restore operations through
the TUI interface. Pressing Ctrl+C or ESC did nothing during execution.

ROOT CAUSE:
- BackupExecutionModel ignored ALL key presses while running (only handled when done)
- RestoreExecutionModel returned tea.Quit but didn't cancel the context
- The operation goroutine kept running in the background with its own context

FIX:
- Added cancel context.CancelFunc to both execution models
- Create child context with WithCancel in New*Execution constructors
- Handle ctrl+c and esc during execution to call cancel()
- Show 'Cancelling...' status while waiting for graceful shutdown
- Show cancel hint in View: 'Press Ctrl+C or ESC to cancel'

The fix works because:
- exec.CommandContext(ctx) will SIGKILL the subprocess when ctx is cancelled
- pg_dump, pg_restore, psql, mysql all get terminated properly
- User sees immediate feedback that cancellation is in progress

internal/tui/backup_exec.go

@@ -20,12 +20,14 @@ type BackupExecutionModel struct {
 	logger       logger.Logger
 	parent       tea.Model
 	ctx          context.Context
+	cancel       context.CancelFunc // Cancel function to stop the operation
 	backupType   string
 	databaseName string
 	ratio        int
 	status       string
 	progress     int
 	done         bool
+	cancelling   bool // True when user has requested cancellation
 	err          error
 	result       string
 	startTime    time.Time
@@ -34,11 +36,14 @@ type BackupExecutionModel struct {
 }
 
 func NewBackupExecution(cfg *config.Config, log logger.Logger, parent tea.Model, ctx context.Context, backupType, dbName string, ratio int) BackupExecutionModel {
+	// Create a cancellable context derived from parent
+	childCtx, cancel := context.WithCancel(ctx)
 	return BackupExecutionModel{
 		config:       cfg,
 		logger:       log,
 		parent:       parent,
-		ctx:          ctx,
+		ctx:          childCtx,
+		cancel:       cancel,
 		backupType:   backupType,
 		databaseName: dbName,
 		ratio:        ratio,
@@ -206,9 +211,21 @@ func (m BackupExecutionModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		return m, nil
 
 	case tea.KeyMsg:
-		if m.done {
-			switch msg.String() {
-			case "enter", "esc", "q":
+		switch msg.String() {
+		case "ctrl+c", "esc":
+			if !m.done && !m.cancelling {
+				// User requested cancellation - cancel the context
+				m.cancelling = true
+				m.status = "⏹️  Cancelling backup... (please wait)"
+				if m.cancel != nil {
+					m.cancel()
+				}
+				return m, nil
+			} else if m.done {
+				return m.parent, nil
+			}
+		case "enter", "q":
+			if m.done {
 				return m.parent, nil
 			}
 		}
@@ -240,7 +257,12 @@ func (m BackupExecutionModel) View() string {
 
 	// Status with spinner
 	if !m.done {
-		s.WriteString(fmt.Sprintf("  %s %s\n", spinnerFrames[m.spinnerFrame], m.status))
+		if m.cancelling {
+			s.WriteString(fmt.Sprintf("  %s %s\n", spinnerFrames[m.spinnerFrame], m.status))
+		} else {
+			s.WriteString(fmt.Sprintf("  %s %s\n", spinnerFrames[m.spinnerFrame], m.status))
+			s.WriteString("\n  ⌨️  Press Ctrl+C or ESC to cancel\n")
+		}
 	} else {
 		s.WriteString(fmt.Sprintf("  %s\n\n", m.status))
 

internal/tui/restore_exec.go

@@ -24,6 +24,7 @@ type RestoreExecutionModel struct {
 	logger            logger.Logger
 	parent            tea.Model
 	ctx               context.Context
+	cancel            context.CancelFunc // Cancel function to stop the operation
 	archive           ArchiveInfo
 	targetDB          string
 	cleanFirst        bool
@@ -44,19 +45,23 @@ type RestoreExecutionModel struct {
 	spinnerFrames []string
 
 	// Results
-	done    bool
-	err     error
-	result  string
-	elapsed time.Duration
+	done       bool
+	cancelling bool // True when user has requested cancellation
+	err        error
+	result     string
+	elapsed    time.Duration
 }
 
 // NewRestoreExecution creates a new restore execution model
 func NewRestoreExecution(cfg *config.Config, log logger.Logger, parent tea.Model, ctx context.Context, archive ArchiveInfo, targetDB string, cleanFirst, createIfMissing bool, restoreType string, cleanClusterFirst bool, existingDBs []string, saveDebugLog bool, workDir string) RestoreExecutionModel {
+	// Create a cancellable context derived from parent
+	childCtx, cancel := context.WithCancel(ctx)
 	return RestoreExecutionModel{
 		config:            cfg,
 		logger:            log,
 		parent:            parent,
-		ctx:               ctx,
+		ctx:               childCtx,
+		cancel:            cancel,
 		archive:           archive,
 		targetDB:          targetDB,
 		cleanFirst:        cleanFirst,
@@ -274,11 +279,32 @@ func (m RestoreExecutionModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 
 	case tea.KeyMsg:
 		switch msg.String() {
-		case "ctrl+c", "q":
-			// Always allow quitting
-			return m.parent, tea.Quit
-
-		case "enter", " ", "esc":
+		case "ctrl+c", "esc":
+			if !m.done && !m.cancelling {
+				// User requested cancellation - cancel the context
+				m.cancelling = true
+				m.status = "⏹️  Cancelling restore... (please wait)"
+				m.phase = "Cancelling"
+				if m.cancel != nil {
+					m.cancel()
+				}
+				return m, nil
+			} else if m.done {
+				return m.parent, nil
+			}
+		case "q":
+			if !m.done && !m.cancelling {
+				m.cancelling = true
+				m.status = "⏹️  Cancelling restore... (please wait)"
+				m.phase = "Cancelling"
+				if m.cancel != nil {
+					m.cancel()
+				}
+				return m, nil
+			} else if m.done {
+				return m.parent, tea.Quit
+			}
+		case "enter", " ":
 			if m.done {
 				return m.parent, nil
 			}