Fix: Interactive backup now shows dynamic status updates during operation

Issue: Interactive backup (single, sample, cluster) showed 'Status: Initializing...'
throughout the entire backup process, identical to the restore issue that was just fixed.

Root cause:
- Status was set once in NewBackupExecution()
- Never updated during the backup process
- Only changed to success/failure at completion
- No visual feedback about backup progress

Solution: Time-based status progression (matching restore pattern)
Added logic in Update() tick handler to change status based on elapsed time:

- 0-2 sec: 'Initializing backup...'

- 2-5 sec: Connection phase:
  - Cluster: 'Connecting to database cluster...'
  - Single/Sample: 'Connecting to database [name]...'

- 5-10 sec: Early backup phase:
  - Cluster: 'Backing up global objects (roles, tablespaces)...'
  - Sample: 'Analyzing tables for sampling (ratio: N)...'
  - Single: 'Dumping database [name]...'

- 10+ sec: Main backup phase:
  - Cluster: 'Backing up cluster databases...'
  - Sample: 'Creating sample backup of [name]...'
  - Single: 'Backing up database [name]...'

Benefits:
- Consistent UX with restore operations
- Different status messages for single/sample/cluster backups
- Shows what stage of backup is running
- Spinner + changing status = clear progress indication
- Better user experience during long cluster backups

Status checked across all TUI operations:
✅ RestoreExecutionModel - Fixed (previous commit)
✅ BackupExecutionModel - Fixed (this commit)
✅ StatusViewModel - Already has proper loading state
✅ OperationsViewModel - Simple view, no long operations

internal/tui/backup_exec.go

@@ -144,6 +144,35 @@ func (m BackupExecutionModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	switch msg := msg.(type) {
 	case backupTickMsg:
 		if !m.done {
+			// Update status based on elapsed time to show progress
+			elapsedSec := int(time.Since(m.startTime).Seconds())
+			
+			if elapsedSec < 2 {
+				m.status = "Initializing backup..."
+			} else if elapsedSec < 5 {
+				if m.backupType == "cluster" {
+					m.status = "Connecting to database cluster..."
+				} else {
+					m.status = fmt.Sprintf("Connecting to database '%s'...", m.databaseName)
+				}
+			} else if elapsedSec < 10 {
+				if m.backupType == "cluster" {
+					m.status = "Backing up global objects (roles, tablespaces)..."
+				} else if m.backupType == "sample" {
+					m.status = fmt.Sprintf("Analyzing tables for sampling (ratio: %d)...", m.ratio)
+				} else {
+					m.status = fmt.Sprintf("Dumping database '%s'...", m.databaseName)
+				}
+			} else {
+				if m.backupType == "cluster" {
+					m.status = "Backing up cluster databases..."
+				} else if m.backupType == "sample" {
+					m.status = fmt.Sprintf("Creating sample backup of '%s'...", m.databaseName)
+				} else {
+					m.status = fmt.Sprintf("Backing up database '%s'...", m.databaseName)
+				}
+			}
+			
 			return m, backupTickCmd()
 		}
 		return m, nil