Implement HTTP timeout configurations and enhance API documentation

- Added optional HTTP server timeout configurations (`HNHMAP_READ_TIMEOUT`, `HNHMAP_WRITE_TIMEOUT`, `HNHMAP_IDLE_TIMEOUT`) to `.env.example` and updated the server initialization in `main.go` to utilize these settings.
- Enhanced API documentation for the `rebuildZooms` endpoint to clarify its background processing and polling mechanism for status updates.
- Updated `configuration.md` to include new timeout environment variables for better configuration guidance.
- Improved error handling in the client for large request bodies, ensuring appropriate responses for oversized payloads.

internal/app/services/admin.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"strconv"
+	"sync"
 
 	"github.com/andyleap/hnh-map/internal/app"
 	"github.com/andyleap/hnh-map/internal/app/store"
@@ -17,6 +18,9 @@ import (
 type AdminService struct {
 	st     *store.Store
 	mapSvc *MapService
+
+	rebuildMu    sync.Mutex
+	rebuildRunning bool
 }
 
 // NewAdminService creates an AdminService with the given store and map service.
@@ -372,3 +376,32 @@ func (s *AdminService) HideMarker(ctx context.Context, markerID string) error {
 func (s *AdminService) RebuildZooms(ctx context.Context) error {
 	return s.mapSvc.RebuildZooms(ctx)
 }
+
+// StartRebuildZooms starts RebuildZooms in a goroutine and returns immediately.
+// RebuildZoomsRunning returns true while the rebuild is in progress.
+func (s *AdminService) StartRebuildZooms() {
+	s.rebuildMu.Lock()
+	if s.rebuildRunning {
+		s.rebuildMu.Unlock()
+		return
+	}
+	s.rebuildRunning = true
+	s.rebuildMu.Unlock()
+	go func() {
+		defer func() {
+			s.rebuildMu.Lock()
+			s.rebuildRunning = false
+			s.rebuildMu.Unlock()
+		}()
+		if err := s.mapSvc.RebuildZooms(context.Background()); err != nil {
+			slog.Error("RebuildZooms background failed", "error", err)
+		}
+	}()
+}
+
+// RebuildZoomsRunning returns true if a rebuild is currently in progress.
+func (s *AdminService) RebuildZoomsRunning() bool {
+	s.rebuildMu.Lock()
+	defer s.rebuildMu.Unlock()
+	return s.rebuildRunning
+}