fix(upload): clear error and higher limit for large files

- raise upload limit to 100 MB
- return 413 file_too_large on MaxBytesError instead of misleading
  "expected multipart form"
- client-side per-file and total size pre-check with a clear message

backend/internal/photos/handlers.go

@@ -1,6 +1,7 @@
 package photos
 
 import (
+	"errors"
 	"io"
 	"net/http"
 	"strconv"
@@ -12,7 +13,7 @@ import (
 	"shared-album/internal/httpx"
 )
 
-const maxUploadSize = 50 << 20
+const maxUploadSize = 100 << 20
 
 type Handler struct {
 	svc *Service
@@ -43,7 +44,12 @@ func (h *Handler) Upload(c *gin.Context) {
 	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, maxUploadSize)
 	form, err := c.MultipartForm()
 	if err != nil {
-		httpx.RespondError(c, httpx.BadRequest("invalid_request", "expected multipart form"))
+		var maxErr *http.MaxBytesError
+		if errors.As(err, &maxErr) {
+			httpx.RespondError(c, httpx.NewError(http.StatusRequestEntityTooLarge, "file_too_large", "files exceed the maximum upload size (100 MB)"))
+			return
+		}
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "invalid multipart form"))
 		return
 	}
 	files := form.File["files"]

frontend/src/lib/components/Uploader.svelte

@@ -14,6 +14,8 @@
 	let progress = $state(0);
 	let error = $state('');
 
+	const MAX_SIZE = 100 * 1024 * 1024;
+
 	export function pick() {
 		fileInput?.click();
 	}
@@ -21,6 +23,16 @@
 	export function upload(files: FileList | File[]) {
 		const list = Array.from(files);
 		if (list.length === 0) return;
+		const tooBig = list.filter((f) => f.size > MAX_SIZE);
+		if (tooBig.length > 0) {
+			error = `Файл слишком большой: ${tooBig.map((f) => f.name).join(', ')}. Максимум 100 МБ.`;
+			return;
+		}
+		const total = list.reduce((sum, f) => sum + f.size, 0);
+		if (total > MAX_SIZE) {
+			error = 'Суммарный размер файлов превышает 100 МБ. Загрузите меньшими порциями.';
+			return;
+		}
 		error = '';
 		busy = true;
 		progress = 0;