feat(learn): + opens a sheet as Claude's, Camera, Photos and Files, and what goes along in rounded rows

Following the developer's review of 3 Nov 2026 (ADR 0021, D67):

- + below the assistant's field, and below a conversation's follow-up,
  opens "Add to your question" as Claude's "Add to session": three big
  tiles side by side, Camera (where the device takes photos) and Photos
  for an assistant reading images, and Files; below them, in the field, a
  row leading to what goes along, showing how far the assistant looks and
  how many parts are chosen.
- Camera and Photos through image_picker (flutter.dev's own): the camera's
  own app and the system's photo picker, no permission asked on Android, a
  file dialog on the desktop, which has no Camera; photos made at most
  2048 pixels a side, read on the device like any file attached.
- What goes along is chosen in rounded rows, as Claude's Permission, in
  place of radio buttons and chips: how far it looks with a tick, private
  studysets with a switch, the parts each with a tick, a card's image with
  its thumbnail.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -2549,5 +2549,13 @@
   "studysetSheetVisibility": "Visibility",
   "@studysetSheetVisibility": {"description": "Heading in a top-level studyset's Edit sheet above its privacy switch (ADR 0019)."},
   "studysetSheetPrivate": "Private",
-  "@studysetSheetPrivate": {"description": "The switch making a top-level studyset private (end-to-end encrypted) in its Edit sheet."}
+  "@studysetSheetPrivate": {"description": "The switch making a top-level studyset private (end-to-end encrypted) in its Edit sheet."},
+  "assistantAddTitle": "Add to your question",
+  "@assistantAddTitle": {"description": "Title of the sheet + opens below the assistant's field, as Claude's \"Add to session\"."},
+  "assistantAddCamera": "Camera",
+  "@assistantAddCamera": {"description": "Tile in +'s sheet: takes a photo with the camera's own app."},
+  "assistantAddPhotos": "Photos",
+  "@assistantAddPhotos": {"description": "Tile in +'s sheet: picks photos from the device."},
+  "assistantAddFiles": "Files",
+  "@assistantAddFiles": {"description": "Tile in +'s sheet: picks files (PDFs, texts, images)."}
 }