feat(learn): Add material no longer offers flashcards from a text (ADR 0021, D56 amended)

The developer's review of 4 Nov 2026. The entry goes from a studyset's
Add material, and with it the sheet for pasting a text
(proposeCardsFromText, _TextSheet), its three texts and proposeCards'
fromStudyset, which only it set to false. A note's and a PDF page's
flashcards stay; their tests now drive the proposals sheet from a note.

Whats-New: Add material no longer offers Flashcards from a text; a note's or a PDF page's flashcards stay.
Whats-New-De: Material hinzufügen bietet keine Karteikarten aus einem Text mehr an; die aus einer Notiz oder einer PDF-Seite bleiben.

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

@@ -2248,10 +2248,6 @@
   "@proposalsFromPage": {"description": "In a PDF's flashcards: has an assistant propose cards from the page shown (D56)."},
   "proposalsFromSelection": "From the selection",
   "@proposalsFromSelection": {"description": "In a PDF's flashcards: has an assistant propose cards from the text selected (D56)."},
-  "proposalsFromText": "Flashcards from a text",
-  "@proposalsFromText": {"description": "Add material: has an assistant propose cards from text pasted (D56)."},
-  "proposalsTextHint": "Paste the text to make flashcards from",
-  "proposalsPropose": "Propose flashcards",
   "settingsSearchEngine": "Search engine",
   "searchEngineDevice": "The device's search",
   "searchEngineCustom": "Your own address",