Fix what the first Android run found

The flow ran on a Pixel 9a and its emulator (2026-10-02); what it found:

- The composer stayed on the card just written after "New flashcard", and
  on the original after "Duplicate": leaving a card changed the state
  before the new one was in it, so the screen took the new card for gone.
  It now waits for the card it asked for.
- Bottom sheets reached under the status bar with the keyboard open
  (useSafeArea).
- The field being written stayed behind the keyboard: the editor scrolls
  only within itself, so the card face now keeps it in view when it opens
  and when the keyboard rises, as a text field does.
- A tap on read-only rich text put a caret in it and opened the keyboard on
  phones, and in the composer never opened the field. RichContentView is
  display only now: no selection, taps go to what surrounds it, a sound's
  button still plays (decided 2026-10-02).
- The card types broke their names on a phone; they are choice chips that
  wrap (decided 2026-10-02).
- The week overview marked days before the person's first activity as
  missed; they show nothing now. An import starts the activity too, without
  counting as studying (decided 2026-10-02).
- A composer preview cut short gave no sign of it; it fades out over its
  last 32 dp, only when cut short (decided 2026-10-02).
- "Isn't on this device yet" showed for any image or sound that failed;
  a file that is here but can't be decoded now says so, and offers no retry.
- The signed-in account card was narrower than the anonymous one.
- The composer's title said "Create flashcards" also when opened on a
  stored card; it says "Edit flashcards in …" then (decided 2026-10-02).
- The Anki fixtures carry a valid PNG and a silent MP3, so they also serve
  to try the import by hand (decided 2026-10-02); regenerated with Anki
  26.9.3.

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

halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -172,6 +172,9 @@
   "composerTitle": "Create flashcards",
   "composerTitleFor": "Create flashcards for \"{title}\"",
   "@composerTitleFor": {"placeholders": {"title": {"type": "String"}}},
+  "composerEditTitle": "Edit flashcards",
+  "composerEditTitleFor": "Edit flashcards in \"{title}\"",
+  "@composerEditTitleFor": {"placeholders": {"title": {"type": "String"}}},
   "composerSaving": "Saving…",
   "composerSaveFailed": "Save failed — retry",
   "composerAllSaved": "All changes saved",
@@ -376,10 +379,12 @@
   "fileImage": "Image",
   "fileSound": "Sound",
   "fileImageUnavailable": "This image isn't on this device yet. It shows once it's uploaded and you're online.",
+  "fileImageUnreadable": "This image can't be shown. Its file may be damaged, or in a format this device can't read.",
   "fileFromElsewhere": "Files from the web aren't shown.",
   "filePlaySound": "Play sound",
   "fileStopSound": "Stop sound",
   "fileSoundUnavailable": "This sound isn't on this device yet. It plays once it's uploaded and you're online.",
+  "fileSoundUnplayable": "This sound can't be played. Its file may be damaged, or in a format this device can't play.",
   "ankiImportMenu": "Import from Anki",
   "ankiImportFileType": "Anki decks",
   "ankiImportTitle": "Import Anki deck",