feat: add Sentry error reporting

Capture command errors and panics with Sentry SDK. DSN injected
at build time via ldflags (dev builds silent, releases report).
Opt-out: UNARR_NO_TELEMETRY=1.

internal/sentry/sentry.go

@@ -0,0 +1,85 @@
+package sentry
+
+import (
+	"os"
+	"runtime"
+	"strings"
+	"time"
+
+	gosentry "github.com/getsentry/sentry-go"
+)
+
+// dsn is injected at build time via ldflags. If empty, Sentry is disabled.
+// Set via: -ldflags "-X github.com/torrentclaw/torrentclaw-cli/internal/sentry.dsn=..."
+var dsn string
+
+const flushTimeout = 2 * time.Second
+
+// Init initializes the Sentry SDK. Call Close() on shutdown to flush events.
+// No-op if telemetry is disabled (UNARR_NO_TELEMETRY=1).
+func Init(version string) {
+	if dsn == "" || os.Getenv("UNARR_NO_TELEMETRY") == "1" {
+		return
+	}
+
+	err := gosentry.Init(gosentry.ClientOptions{
+		Dsn:              dsn,
+		Release:          "unarr@" + version,
+		Environment:      environment(version),
+		AttachStacktrace: true,
+	})
+	if err != nil {
+		return
+	}
+
+	gosentry.ConfigureScope(func(scope *gosentry.Scope) {
+		scope.SetTag("os", runtime.GOOS)
+		scope.SetTag("arch", runtime.GOARCH)
+		scope.SetTag("go_version", runtime.Version())
+	})
+}
+
+// Close flushes pending events with a timeout.
+func Close() {
+	gosentry.Flush(flushTimeout)
+}
+
+// CaptureError sends a non-fatal error to Sentry with optional command context.
+func CaptureError(err error, command string) {
+	if err == nil {
+		return
+	}
+
+	gosentry.WithScope(func(scope *gosentry.Scope) {
+		if command != "" {
+			scope.SetTag("command", command)
+		}
+		gosentry.CaptureException(err)
+	})
+}
+
+// RecoverPanic captures a panic and re-panics after reporting.
+// Usage: defer sentry.RecoverPanic()
+func RecoverPanic() {
+	if r := recover(); r != nil {
+		gosentry.CurrentHub().Recover(r)
+		gosentry.Flush(flushTimeout)
+
+		// Re-panic so the user sees the stack trace and the process exits non-zero
+		panic(r)
+	}
+}
+
+// SetUser sets the user context (agent ID) for all subsequent events.
+func SetUser(agentID string) {
+	gosentry.ConfigureScope(func(scope *gosentry.Scope) {
+		scope.SetUser(gosentry.User{ID: agentID})
+	})
+}
+
+func environment(version string) string {
+	if version == "" || version == "dev" || strings.HasSuffix(version, "-dev") {
+		return "development"
+	}
+	return "production"
+}