Fix: defensive frontend + panic recovery logging middleware

Frontend:
- JobDetail loadLogs: fallback to [] when API returns null
- JobDetail loadJob: pairs ?? [] guard on /api/sync-pairs 500
- JobHistory: Array.isArray guard on job list response
- api client: return undefined for null body instead of throwing

Backend:
- handlers_jobs GetLog: return [] instead of null when no log rows
- router: custom recoverer middleware that logs panics to slog
  with full stack trace, method, and path

internal/api/handlers_jobs.go

@@ -166,7 +166,11 @@ func (h *JobHandler) GetLog(w http.ResponseWriter, r *http.Request) {
 
 	count, _ := logRepo.CountByJobID(id)
 	w.Header().Set("X-Total-Count", fmt.Sprintf("%d", count))
-	writeJSON(w, logs)
+	if logs == nil {
+		writeJSON(w, []any{})
+	} else {
+		writeJSON(w, logs)
+	}
 }
 
 func (h *JobHandler) DownloadLog(w http.ResponseWriter, r *http.Request) {

internal/api/router.go

@@ -2,7 +2,9 @@ package api
 
 import (
 	"database/sql"
+	"log/slog"
 	"net/http"
+	"runtime/debug"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
@@ -26,7 +28,7 @@ func NewServer(cfg *config.Config, db *sql.DB, engine *syncengine.Engine) *Serve
 	r.Use(middleware.RequestID)
 	r.Use(middleware.RealIP)
 	r.Use(middleware.Logger)
-	r.Use(middleware.Recoverer)
+	r.Use(recoverer)
 
 	s := &Server{router: r, cfg: cfg, engine: engine}
 
@@ -101,3 +103,22 @@ func NewServer(cfg *config.Config, db *sql.DB, engine *syncengine.Engine) *Serve
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	s.router.ServeHTTP(w, r)
 }
+
+func recoverer(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			if err := recover(); err != nil {
+				slog.Error("panic recovered",
+					"error", err,
+					"stack", string(debug.Stack()),
+					"method", r.Method,
+					"path", r.URL.Path,
+				)
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusInternalServerError)
+				http.Error(w, `{"error":"internal server error"}`, http.StatusInternalServerError)
+			}
+		}()
+		next.ServeHTTP(w, r)
+	})
+}