feat: improve daemon resilience, streaming, and usenet downloads

- Add daemon state persistence and stale resume file cleanup
- Add TriggerPoll for WebSocket resume actions
- Improve stream server with graceful shutdown and connection tracking
- Add desktop notifications for download completion
- Add media file organization with Movies/TV Shows detection
- Improve usenet downloader with progress tracking and resume support
- Add self-update package with GitHub release verification
- Downgrade tablewriter to v0.0.5 (v1.x API breaking change)

internal/engine/notify_test.go

@@ -0,0 +1,46 @@
+package engine
+
+import "testing"
+
+func TestEscapePowerShell(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"hello", "hello"},
+		{"it's done", "it''s done"},
+		{"Tom's 'file'", "Tom''s ''file''"},
+		{"no quotes", "no quotes"},
+		{"", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := escapePowerShell(tt.input)
+			if got != tt.want {
+				t.Errorf("escapePowerShell(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestEscapeAppleScript(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"hello", "hello"},
+		{`say "hi"`, `say \"hi\"`},
+		{`back\slash`, `back\\slash`},
+		{"", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := escapeAppleScript(tt.input)
+			if got != tt.want {
+				t.Errorf("escapeAppleScript(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}