feat(learn): the assistant's button folded on Home too, the conversation at full height folding into it, and smaller fixes from the developer's list (ADR 0021, D64, D65)

- Home's assistant starts folded into its button at the lower left, as
  in the Library, where a field stood at its foot.
- The button has Material 3's floating action button shape (a rounded
  square) rather than a circle, its gradient ring kept.
- On a studyset below expanded windows it stands in one row with Add
  material and Study rather than above them.
- While studying, the ratings below the card make way while its field
  is open rather than standing under it.
- The conversation opens at the window's full height, its header above
  the list, so a drag on the header moves the sheet and a drag on the
  list scrolls it. Close ends the conversation; any other way out folds
  it into the button (ConversationDockCubit, above the router), its
  answer still coming, until any button opens it again or another
  conversation starts.
- An answer's Copy icon lines up with the answer's text.
- A sense's grammar notes run on after its glosses as one flowing text,
  so a short note such as "n" no longer takes a line of its own.
- A card's hints show their count in a grey badge beside the title, so
  it no longer reads as the hint's number.

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

@@ -755,7 +755,7 @@
   "cardExplanation": "Explanation",
   "cardAddExplanation": "Add explanation",
   "cardRemoveExplanation": "Remove explanation",
-  "cardHintsSheetTitle": "{count, plural, =1{Hint} other{Hints  {count}}}",
+  "cardHintsSheetTitle": "{count, plural, =1{Hint} other{Hints}}",
   "@cardHintsSheetTitle": {"placeholders": {"count": {"type": "int"}}},
   "cardPreviousHint": "Previous hint",
   "cardNextHint": "Next hint",
@@ -2120,6 +2120,10 @@
   "settingsAskAssistantSubtitle": "Off unless you turn it on. Adds a field on Home and a button in the Library, on a studyset and while studying. A question opens as a web search, with only the parts of a card you choose; nothing is sent from here.",
   "assistantOpen": "Search the web",
   "assistantClose": "Close",
+  "assistantBackToConversation": "Back to the conversation",
+  "@assistantBackToConversation": {
+    "description": "The tooltip of the assistant's button while a conversation is folded away into it, its sheet swiped down."
+  },
 
 
   "assistantLineFront": "Front: {text}",