feat: inline conversion with status updates, cwebp support, v0.1.4

- Conversion now happens inline on the file list — status column updates
  from idle → converting... → done/error in place (no separate screen)
- Fixed value-receiver bug in convertNext() that prevented 'converting'
  status from being displayed
- Added cwebp fallback for PNG/JPEG → WebP (ffmpeg webp encoder often
  missing on macOS)
- Format selector arrows hidden during conversion/results states
- Simplified to 2 states: stateFileList + stateResults
- Added tests for conversion state machine and view rendering

cli/internal/tui/model_test.go

@@ -0,0 +1,145 @@
+package tui
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+func TestInlineConversionStateMachine(t *testing.T) {
+	// Find a test PNG file
+	testFile := filepath.Join("..", "..", "..", "public", "logo.png")
+	if _, err := os.Stat(testFile); err != nil {
+		t.Skipf("test file not found: %s", testFile)
+	}
+
+	outDir := t.TempDir()
+	m := New([]string{testFile}, outDir)
+	m.width = 80
+	m.height = 24
+
+	// Verify initial state
+	if len(m.files) != 1 {
+		t.Fatalf("expected 1 file, got %d", len(m.files))
+	}
+	if m.state != stateFileList {
+		t.Fatalf("expected stateFileList, got %d", m.state)
+	}
+	if m.files[0].status != "idle" {
+		t.Fatalf("expected idle status, got %s", m.files[0].status)
+	}
+	if !m.files[0].selected {
+		t.Fatal("expected file to be selected by default")
+	}
+
+	t.Logf("File: %s -> %s (selected: %v)", m.files[0].name, m.files[0].targetFormat, m.files[0].selected)
+
+	// Simulate pressing 'c' to start conversion
+	newModel, cmd := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune{'c'}})
+	m = newModel.(Model)
+
+	if m.state != stateFileList {
+		t.Fatalf("expected to stay on stateFileList during conversion, got %d", m.state)
+	}
+	if m.totalToConv != 1 {
+		t.Fatalf("expected totalToConv=1, got %d", m.totalToConv)
+	}
+	if m.files[0].status != "converting" {
+		t.Fatalf("expected 'converting' status after pressing c, got '%s'", m.files[0].status)
+	}
+
+	t.Log("Status correctly set to 'converting' — inline update works!")
+
+	// Execute the conversion command
+	if cmd == nil {
+		t.Fatal("expected a conversion command, got nil")
+	}
+	msg := cmd()
+
+	// Process the result
+	newModel, _ = m.Update(msg)
+	m = newModel.(Model)
+
+	if m.state != stateResults {
+		t.Fatalf("expected stateResults after all conversions done, got %d", m.state)
+	}
+	if m.files[0].status != "done" {
+		t.Fatalf("expected 'done' status, got '%s' (error: %s)", m.files[0].status, m.files[0].error)
+	}
+	if m.converted != 1 {
+		t.Fatalf("expected converted=1, got %d", m.converted)
+	}
+
+	// Check output file exists
+	info, err := os.Stat(m.files[0].outputPath)
+	if err != nil {
+		t.Fatalf("output file not found: %v", err)
+	}
+
+	t.Logf("Conversion complete: %s (%d bytes)", m.files[0].outputPath, info.Size())
+
+	// Test 'esc' to go back to file list
+	newModel, _ = m.Update(tea.KeyMsg{Type: tea.KeyEscape})
+	m = newModel.(Model)
+
+	if m.state != stateFileList {
+		t.Fatalf("expected stateFileList after esc, got %d", m.state)
+	}
+	if m.files[0].status != "idle" {
+		t.Fatalf("expected status reset to 'idle' after esc, got '%s'", m.files[0].status)
+	}
+
+	t.Log("State machine verified: idle -> converting -> done -> idle (via esc)")
+}
+
+func TestViewRendersDuringConversion(t *testing.T) {
+	testFile := filepath.Join("..", "..", "..", "public", "logo.png")
+	if _, err := os.Stat(testFile); err != nil {
+		t.Skipf("test file not found: %s", testFile)
+	}
+
+	m := New([]string{testFile}, t.TempDir())
+	m.width = 80
+	m.height = 24
+
+	// Render initial state
+	view := m.View()
+	if view == "" {
+		t.Fatal("empty view")
+	}
+	if !containsStr(view, "idle") {
+		t.Error("initial view should contain 'idle' status")
+	}
+	if !containsStr(view, "Convert 1 files") {
+		t.Error("initial view should contain convert button")
+	}
+
+	// Start conversion
+	newModel, _ := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune{'c'}})
+	m = newModel.(Model)
+
+	view = m.View()
+	if !containsStr(view, "converting") {
+		t.Error("view during conversion should contain 'converting' status")
+	}
+	if !containsStr(view, "Converting 0/1") {
+		t.Errorf("view during conversion should show progress, got:\n%s", view)
+	}
+
+	t.Log("View renders correctly during conversion")
+}
+
+func containsStr(haystack, needle string) bool {
+	return len(haystack) > 0 && len(needle) > 0 && contains(haystack, needle)
+}
+
+func contains(s, substr string) bool {
+	for i := 0; i <= len(s)-len(substr); i++ {
+		if s[i:i+len(substr)] == substr {
+			return true
+		}
+	}
+	return false
+}