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/store/db.go

@@ -17,7 +17,9 @@ func New(db *bbolt.DB) *Store {
 	return &Store{db: db}
 }
 
-// View runs fn in a read-only transaction. Checks context before starting.
+// View runs fn in a read-only transaction. It checks context before starting.
+// Long-running callbacks (e.g. large ForEach or ForEachTile) should check ctx.Done()
+// periodically and return ctx.Err() to abort early when the context is cancelled.
 func (s *Store) View(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	select {
 	case <-ctx.Done():
@@ -27,7 +29,8 @@ func (s *Store) View(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	}
 }
 
-// Update runs fn in a read-write transaction. Checks context before starting.
+// Update runs fn in a read-write transaction. It checks context before starting.
+// Long-running callbacks should check ctx.Done() periodically and return ctx.Err() to abort.
 func (s *Store) Update(ctx context.Context, fn func(tx *bbolt.Tx) error) error {
 	select {
 	case <-ctx.Done():
@@ -284,6 +287,30 @@ func (s *Store) GetTile(tx *bbolt.Tx, mapID, zoom int, coordKey string) []byte {
 	return zoomB.Get([]byte(coordKey))
 }
 
+// GetTiles returns raw JSON for multiple tiles in the same map/zoom in one transaction.
+// Keys that are not found are omitted from the result. Coord keys are in the form "x_y".
+func (s *Store) GetTiles(tx *bbolt.Tx, mapID, zoom int, coordKeys []string) map[string][]byte {
+	out := make(map[string][]byte, len(coordKeys))
+	tiles := tx.Bucket(BucketTiles)
+	if tiles == nil {
+		return out
+	}
+	mapB := tiles.Bucket([]byte(strconv.Itoa(mapID)))
+	if mapB == nil {
+		return out
+	}
+	zoomB := mapB.Bucket([]byte(strconv.Itoa(zoom)))
+	if zoomB == nil {
+		return out
+	}
+	for _, k := range coordKeys {
+		if v := zoomB.Get([]byte(k)); v != nil {
+			out[k] = v
+		}
+	}
+	return out
+}
+
 // PutTile stores a tile entry (creates nested buckets as needed).
 func (s *Store) PutTile(tx *bbolt.Tx, mapID, zoom int, coordKey string, raw []byte) error {
 	tiles, err := tx.CreateBucketIfNotExists(BucketTiles)