feat(agent): add crash logs and watchdog startup

- Recover panics to disk for diagnostics
- Add 5-minute watchdog task with startup
- Add -ensure flag to start detached agent
- Add script to pull remote folder via API

lib/crashlog/crashlog_test.go

@@ -0,0 +1,38 @@
+package crashlog
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"tea.chunkbyte.com/kato/go-worm/lib/config"
+)
+
+func TestWrite(t *testing.T) {
+	base := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", base)
+	t.Setenv("APPDATA", base)
+
+	if err := write("test", "boom", []byte("trace")); err != nil {
+		t.Fatal(err)
+	}
+	dir := filepath.Join(base, config.AppDataDir, config.LogsSubdir)
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(entries) != 1 {
+		t.Fatalf("entries = %d, want 1", len(entries))
+	}
+	data, err := os.ReadFile(filepath.Join(dir, entries[0].Name()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	text := string(data)
+	for _, part := range []string{"kind: test", "detail: boom", "trace", config.Version} {
+		if !strings.Contains(text, part) {
+			t.Fatalf("log missing %q: %s", part, text)
+		}
+	}
+}