fix(uploads): apply configured max file size to guest uploads (#613 follow-up)

The admin's Settings → General → "Max File Size (MB)" value
(general_max_file_size_mb) never applied to guest gallery uploads — the guest
route hardcoded multer's per-file cap at 50MB (gallery.js) and the guest UI
hardcoded the same 50MB client-side guard and "max 50MB" hint text. So a guest
could not upload a large video even when the admin raised the limit (reported by
mat1990dj on #613). Same class as the file-count miss fixed in #614, for size.

- uploadSettings.js: new getMaxFileSizeMb()/getMaxFileSizeBytes() reading
  general_max_file_size_mb (default 50MB, cached 60s, clamped to a 10GB ceiling),
  mirroring getMaxFilesPerUpload.
- gallery.js (guest upload): multer limits.fileSize now resolves from the
  setting; a LIMIT_FILE_SIZE error returns an actionable "max N MB" message.
- publicSettings.js: exposes general_max_file_size_mb (default 50) so the gallery
  UI can render the real limit and guard client-side before an oversized POST.
- UserPhotoUpload.tsx: reads the limit, uses it for the client-side size guard,
  and passes it to the requirements hint. The "max 50MB" literal in
  upload.fileRequirements is now interpolated ({{sizeLimit}}) across all 8
  locales; adds upload.fileTooLarge (en/de; others fall back to en).

Scope: guest path only (the reported gap). The admin path keeps its generous
10GB cap — admins are trusted and default 50MB would otherwise regress large
admin video uploads. Format and batch-size limits already work correctly and are
untouched. Adds SQLite-backed unit tests for the new getter.

Verified end-to-end on a booted instance: admin sets 500MB → persisted → public
settings exposes 500 → guest multer sources its cap from it.

frontend/src/i18n/locales/de.json

@@ -159,7 +159,7 @@
     "noCategory": "Keine Kategorie",
     "eventSpecific": "(Veranstaltungsspezifisch)",
     "clickToUpload": "Klicken zum Hochladen oder per Drag & Drop",
-    "fileRequirements": "JPEG, PNG oder WebP (max. 50MB pro Datei, {{limit}} Dateien pro Upload)",
+    "fileRequirements": "JPEG, PNG oder WebP (max. {{sizeLimit}}MB pro Datei, {{limit}} Dateien pro Upload)",
     "selectedFiles": "Ausgewählte Dateien",
     "uploading": "Wird hochgeladen...",
     "transferring": "Übertragung",
@@ -192,7 +192,8 @@
     "processingFailed_one": "{{count}} Foto konnte nicht verarbeitet werden",
     "processingFailed_other": "{{count}} Fotos konnten nicht verarbeitet werden",
     "uploadingChunks_one": "{{count}} Teil wird hochgeladen",
-    "uploadingChunks_other": "{{count}} Teile werden hochgeladen"
+    "uploadingChunks_other": "{{count}} Teile werden hochgeladen",
+    "fileTooLarge": "Datei zu groß: {{name}} (max. {{limit}}MB)"
   },
   "navigation": {
     "dashboard": "Dashboard",

frontend/src/i18n/locales/en.json

@@ -159,7 +159,7 @@
     "noCategory": "No category",
     "eventSpecific": "(Event specific)",
     "clickToUpload": "Click to upload or drag and drop",
-    "fileRequirements": "JPEG, PNG or WebP (max 50MB per file, {{limit}} files per upload)",
+    "fileRequirements": "JPEG, PNG or WebP (max {{sizeLimit}}MB per file, {{limit}} files per upload)",
     "selectedFiles": "Selected files",
     "uploading": "Uploading...",
     "transferring": "Transferring",
@@ -192,7 +192,8 @@
     "processingFailed_one": "{{count}} photo failed to process",
     "processingFailed_other": "{{count}} photos failed to process",
     "uploadingChunks_one": "{{count}} chunk uploading",
-    "uploadingChunks_other": "{{count}} chunks uploading"
+    "uploadingChunks_other": "{{count}} chunks uploading",
+    "fileTooLarge": "File too large: {{name}} (max {{limit}}MB)"
   },
   "navigation": {
     "dashboard": "Dashboard",

frontend/src/i18n/locales/es.json

@@ -126,7 +126,7 @@
     "noCategory": "Sin categoría",
     "eventSpecific": "(Específico del evento)",
     "clickToUpload": "Haz clic para subir o arrastra y suelta",
-    "fileRequirements": "JPEG, PNG o WebP (máx. 50MB por archivo, {{limit}} archivos por subida)",
+    "fileRequirements": "JPEG, PNG o WebP (máx. {{sizeLimit}}MB por archivo, {{limit}} archivos por subida)",
     "fileRequirementsMedia": "Imágenes JPEG, PNG o WebP y videos MP4/MOV/WEBM (máx. 50MB por archivo, {{limit}} archivos por subida)",
     "unsupportedFiles": "Algunos archivos se omitieron porque el formato no es compatible (usa JPEG/PNG/WebP/MP4/MOV/WEBM).",
     "selectedFiles": "Archivos seleccionados",

frontend/src/i18n/locales/fr.json

@@ -131,7 +131,7 @@
     "noCategory": "Aucune catégorie",
     "eventSpecific": "(Spécifique à l'événement)",
     "clickToUpload": "Cliquez pour téléverser ou glissez-déposez",
-    "fileRequirements": "JPEG, PNG ou WebP (max 50 Mo par fichier, {{limit}} fichiers par téléversement)",
+    "fileRequirements": "JPEG, PNG ou WebP (max {{sizeLimit}} Mo par fichier, {{limit}} fichiers par téléversement)",
     "selectedFiles": "Fichiers sélectionnés",
     "uploading": "Téléversement en cours...",
     "transferring": "Transfert en cours",

frontend/src/i18n/locales/nl.json

@@ -131,7 +131,7 @@
     "noCategory": "Geen categorie",
     "eventSpecific": "(Evenement-specifiek)",
     "clickToUpload": "Klik om te uploaden of sleep bestanden hierheen",
-    "fileRequirements": "JPEG, PNG of WebP (max. 50 MB per bestand, {{limit}} bestanden per upload)",
+    "fileRequirements": "JPEG, PNG of WebP (max. {{sizeLimit}} MB per bestand, {{limit}} bestanden per upload)",
     "selectedFiles": "Geselecteerde bestanden",
     "uploading": "Uploaden...",
     "uploadComplete": "Upload voltooid!",

frontend/src/i18n/locales/pt.json

@@ -131,7 +131,7 @@
     "noCategory": "Sem categoria",
     "eventSpecific": "(Específico do evento)",
     "clickToUpload": "Clique para enviar ou arraste e solte",
-    "fileRequirements": "JPEG, PNG ou WebP (máx. 50MB por arquivo, {{limit}} arquivos por envio)",
+    "fileRequirements": "JPEG, PNG ou WebP (máx. {{sizeLimit}}MB por arquivo, {{limit}} arquivos por envio)",
     "selectedFiles": "Arquivos selecionados",
     "uploading": "Enviando...",
     "uploadComplete": "Envio concluído!",

frontend/src/i18n/locales/ru.json

@@ -131,7 +131,7 @@
     "noCategory": "Без категории",
     "eventSpecific": "(Для конкретного события)",
     "clickToUpload": "Нажмите для загрузки или перетащите файлы",
-    "fileRequirements": "JPEG, PNG или WebP (макс. 50 МБ на файл, {{limit}} файлов за загрузку)",
+    "fileRequirements": "JPEG, PNG или WebP (макс. {{sizeLimit}} МБ на файл, {{limit}} файлов за загрузку)",
     "selectedFiles": "Выбранные файлы",
     "uploading": "Загрузка...",
     "uploadComplete": "Загрузка завершена!",

frontend/src/i18n/locales/sl.json

@@ -131,7 +131,7 @@
     "noCategory": "Brez kategorije",
     "eventSpecific": "(specifično za dogodek)",
     "clickToUpload": "Kliknite za nalaganje ali povlecite in spustite",
-    "fileRequirements": "JPEG, PNG ali WebP (največ 50 MB na datoteko, {{limit}} datotek na nalaganje)",
+    "fileRequirements": "JPEG, PNG ali WebP (največ {{sizeLimit}} MB na datoteko, {{limit}} datotek na nalaganje)",
     "selectedFiles": "Izbrane datoteke",
     "uploading": "Nalaganje...",
     "transferring": "Prenašanje",