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/export.go

@@ -35,14 +35,23 @@ func NewExportService(st *store.Store, mapSvc *MapService) *ExportService {
 	return &ExportService{st: st, mapSvc: mapSvc}
 }
 
-// Export writes all map data as a ZIP archive to the given writer.
-func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
-	zw := zip.NewWriter(w)
-	defer zw.Close()
+// exportEntry describes a single grid PNG to copy into the ZIP (collected inside a read-only View).
+type exportEntry struct {
+	ZipPath  string // e.g. "1/grid1.png"
+	FilePath string // absolute path on disk
+}
 
-	return s.st.Update(ctx, func(tx *bbolt.Tx) error {
-		maps := map[int]mapData{}
-		gridMap := map[string]int{}
+// Export writes all map data as a ZIP archive to the given writer.
+// It uses a read-only View to collect data, then builds the ZIP outside the transaction
+// so that the write lock is not held during file I/O.
+func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
+	var maps map[int]mapData
+	var gridMap map[string]int
+	var filesToCopy []exportEntry
+
+	if err := s.st.View(ctx, func(tx *bbolt.Tx) error {
+		maps = map[int]mapData{}
+		gridMap = map[string]int{}
 
 		grids := tx.Bucket(store.BucketGrids)
 		if grids == nil {
@@ -54,6 +63,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 		}
 
 		if err := grids.ForEach(func(k, v []byte) error {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
 			gd := app.GridData{}
 			if err := json.Unmarshal(v, &gd); err != nil {
 				return err
@@ -84,17 +98,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 			if err := json.Unmarshal(tdraw, &td); err != nil {
 				return err
 			}
-			fw, err := zw.Create(fmt.Sprintf("%d/%s.png", gd.Map, gd.ID))
-			if err != nil {
-				return err
-			}
-			f, err := os.Open(filepath.Join(s.mapSvc.GridStorage(), td.File))
-			if err != nil {
-				return err
-			}
-			_, err = io.Copy(fw, f)
-			f.Close()
-			return err
+			filesToCopy = append(filesToCopy, exportEntry{
+				ZipPath:  fmt.Sprintf("%d/%s.png", gd.Map, gd.ID),
+				FilePath: filepath.Join(s.mapSvc.GridStorage(), td.File),
+			})
+			return nil
 		}); err != nil {
 			return err
 		}
@@ -104,6 +112,11 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 			markersgrid := markersb.Bucket(store.BucketMarkersGrid)
 			if markersgrid != nil {
 				markersgrid.ForEach(func(k, v []byte) error {
+					select {
+					case <-ctx.Done():
+						return ctx.Err()
+					default:
+					}
 					marker := app.Marker{}
 					if json.Unmarshal(v, &marker) != nil {
 						return nil
@@ -115,16 +128,41 @@ func (s *ExportService) Export(ctx context.Context, w io.Writer) error {
 				})
 			}
 		}
-
-		for mapid, md := range maps {
-			fw, err := zw.Create(fmt.Sprintf("%d/grids.json", mapid))
-			if err != nil {
-				return err
-			}
-			json.NewEncoder(fw).Encode(md)
-		}
 		return nil
-	})
+	}); err != nil {
+		return err
+	}
+
+	// Build ZIP outside the transaction so the write lock is not held during file I/O.
+	zw := zip.NewWriter(w)
+	defer zw.Close()
+
+	for _, e := range filesToCopy {
+		fw, err := zw.Create(e.ZipPath)
+		if err != nil {
+			return err
+		}
+		f, err := os.Open(e.FilePath)
+		if err != nil {
+			return err
+		}
+		_, err = io.Copy(fw, f)
+		f.Close()
+		if err != nil {
+			return err
+		}
+	}
+
+	for mapid, md := range maps {
+		fw, err := zw.Create(fmt.Sprintf("%d/grids.json", mapid))
+		if err != nil {
+			return err
+		}
+		if err := json.NewEncoder(fw).Encode(md); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // Merge imports map data from a ZIP file.