feat(12.2-04): add the fileupload field with deferred uploads on the form session key

- sessionKey.ts: one 32-byte base64url key per form mount, sent only in headers
- api/files.ts: FileRoutes over the record and child file routes, XHR upload with progress, 401 refresh and retry
- FileuploadField and FileCaptionModal per UI-SPEC section 3: dropzone, image grid, rows, per-item states, client pre-checks, reorder, protected previews
- FormView provides FORM_SESSION, counts pending changes as dirty and sends X-Session-Key on create and update
- fileupload lang keys in en and pl, admin-spa docs note, deferred smoke test, rebuilt dist

modules/phrasebook/backend/lang/en/lang.yaml

@@ -104,6 +104,42 @@ extension:
   widget_failed: This control could not be loaded. Refresh the page; if it happens again, check the plugin's assets.
   partial_failed: This section could not be loaded. Refresh the page to try again.
   action_failed: The action could not be completed. Please try again.
+fileupload:
+  attachment: Attachment details
+  help: Add a title and description for this attachment.
+  title_label: Title
+  description_label: Description
+  default_prompt: Drag a file here or click to upload
+  default_prompt_many: Drag files here or click to upload
+  upload_file: Upload file
+  replace_file: Replace file
+  remove_file: Remove file
+  upload_error: Upload error
+  upload_failed: The file could not be uploaded. Try again.
+  retry: Retry
+  too_large: ":name is larger than :size. Choose a smaller file."
+  wrong_type: ":name is not an allowed file type. Allowed: :types."
+  too_many:
+    one: "File limit reached (:max). :count file was not added."
+    other: "File limit reached (:max). :count files were not added."
+  limits_types: "Allowed: :types"
+  limits_size: "up to :size"
+  limits_count: "Files: :current of :max"
+  uploading: "Uploading… :percent%"
+  queued: Waiting…
+  unsaved: Unsaved
+  move: "Move: :name"
+  moved: "Moved :name to position :position of :total."
+  reorder_failed: The new order could not be saved. The previous order is back.
+  edit_details: "Edit details: :name"
+  download: "Download: :name"
+  open_preview: "Open: :name"
+  preview_unavailable: No preview
+  load_failed: The files could not be loaded. Refresh the page to try again.
+  cancel_upload: "Cancel upload: :name"
+  details_saved: Attachment details saved
+  details_submit: Save details
+  empty: No files
 messages:
   list:
     record_count: