feat(app): report what is wrong with a card, and bury cards from the list

- "Report an error", from a card's menu while studying or in the list:
  a category (typo, grammar, content, other) and a note. The card is
  marked to be fixed, and still studied; the list shows the category
  (the note on hover), and "Resolve report" takes it back. A report is
  a revision of the card, so it follows it to every device.
- The list buries a card until tomorrow and brings it back ("Unbury"),
  showing "Buried" meanwhile.
- Each of these says so with an Undo.

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_de.arb

@@ -356,6 +356,22 @@
   "cardNextHint": "Nächster Hinweis",
   "cardReport": "Meldung",
   "cardSenses": "Wortbedeutungen",
+  "cardReportTitle": "Fehler melden",
+  "cardReportSubtitle": "Markiere diese Karte, um sie später zu finden und zu korrigieren.",
+  "cardReportTypo": "Tippfehler",
+  "cardReportGrammar": "Grammatik",
+  "cardReportContent": "Inhalt",
+  "cardReportOther": "Sonstiges",
+  "cardReportNote": "Notiz",
+  "cardReportNoteHint": "Was muss korrigiert werden?",
+  "cardReportSubmit": "Melden",
+  "cardReported": "Zur Korrektur markiert",
+  "cardResolveReport": "Meldung erledigen",
+  "cardReportResolved": "Meldung erledigt",
+  "cardBuriedBadge": "Zurückgestellt",
+  "cardUnbury": "Zurückstellung aufheben",
+  "cardTileBuried": "Karteikarte bis morgen zurückgestellt",
+  "cardTileUnburied": "Karteikarte nicht mehr zurückgestellt",
   "cardFilterTooltip": "Filter",
   "cardFilterTitle": "Filter",
   "cardFilterTag": "Tag",