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/agent/state_test.go

@@ -0,0 +1,106 @@
+package agent
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestWriteAndReadState(t *testing.T) {
+	// Override the state file path for testing
+	tmpDir := t.TempDir()
+	origFn := stateFilePathFn
+	stateFilePathFn = func() string { return filepath.Join(tmpDir, "daemon.state.json") }
+	defer func() { stateFilePathFn = origFn }()
+
+	state := &DaemonState{
+		AgentID:         "agent-123",
+		Status:          "running",
+		Version:         "1.0.0",
+		PID:             12345,
+		StartedAt:       time.Now().Truncate(time.Second),
+		LastHeartbeat:   time.Now().Truncate(time.Second),
+		ActiveTasks:     3,
+		CompletedCount:  10,
+		FailedCount:     2,
+		TotalDownloaded: 1024 * 1024 * 500,
+		MethodStats:     map[string]int{"torrent": 8, "debrid": 2},
+	}
+
+	WriteState(state)
+
+	read := ReadState()
+	if read == nil {
+		t.Fatal("ReadState() returned nil")
+	}
+	if read.AgentID != "agent-123" {
+		t.Errorf("AgentID = %q, want agent-123", read.AgentID)
+	}
+	if read.Status != "running" {
+		t.Errorf("Status = %q, want running", read.Status)
+	}
+	if read.Version != "1.0.0" {
+		t.Errorf("Version = %q, want 1.0.0", read.Version)
+	}
+	if read.PID != 12345 {
+		t.Errorf("PID = %d, want 12345", read.PID)
+	}
+	if read.ActiveTasks != 3 {
+		t.Errorf("ActiveTasks = %d, want 3", read.ActiveTasks)
+	}
+	if read.CompletedCount != 10 {
+		t.Errorf("CompletedCount = %d, want 10", read.CompletedCount)
+	}
+	if read.MethodStats["torrent"] != 8 {
+		t.Errorf("MethodStats[torrent] = %d, want 8", read.MethodStats["torrent"])
+	}
+}
+
+func TestReadStateNotFound(t *testing.T) {
+	tmpDir := t.TempDir()
+	origFn := stateFilePathFn
+	stateFilePathFn = func() string { return filepath.Join(tmpDir, "nonexistent.json") }
+	defer func() { stateFilePathFn = origFn }()
+
+	state := ReadState()
+	if state != nil {
+		t.Errorf("ReadState() = %+v, want nil for missing file", state)
+	}
+}
+
+func TestRemoveState(t *testing.T) {
+	tmpDir := t.TempDir()
+	origFn := stateFilePathFn
+	stateFilePathFn = func() string { return filepath.Join(tmpDir, "daemon.state.json") }
+	defer func() { stateFilePathFn = origFn }()
+
+	WriteState(&DaemonState{AgentID: "test"})
+
+	// Verify file exists
+	path := StateFilePath()
+	if _, err := os.Stat(path); err != nil {
+		t.Fatalf("state file should exist: %v", err)
+	}
+
+	RemoveState()
+
+	if _, err := os.Stat(path); !os.IsNotExist(err) {
+		t.Error("state file should be removed after RemoveState()")
+	}
+}
+
+func TestReadStateCorruptedJSON(t *testing.T) {
+	tmpDir := t.TempDir()
+	origFn := stateFilePathFn
+	path := filepath.Join(tmpDir, "daemon.state.json")
+	stateFilePathFn = func() string { return path }
+	defer func() { stateFilePathFn = origFn }()
+
+	os.WriteFile(path, []byte("not valid json{{{"), 0o644)
+
+	state := ReadState()
+	if state != nil {
+		t.Errorf("ReadState() should return nil for corrupted JSON, got %+v", state)
+	}
+}