feat(app): the studyset screen laid out as before

The Study pill reads "Learn 12 flashcards" in the app bar and "Learn 12"
floating, "Study" with nothing due, and is off with nothing to study,
saying so. With a path not finished, a chevron beside it offers to start
or continue the path: a menu in the app bar, a Study mode sheet on
phones. The floating bar rises above the licence line, which takes two
lines at most.

Add material offers a path, flashcards, a note and a PDF, in that order;
imports moved to the options' Import content, which asks for a learning
path or an Anki deck. The options read Edit, Move, Study options, Import
content, Reset progress, Archive, Delete. The bibliography is an outlined
round button above the content, and on phones at the foot of the topics.

The tabs sit on a line of their own across the card, what the tab shown
offers beside them: the flashcards' filter and options, and on the paths
Reorder once there are two, which turns them into handles to drag. An
empty tab says so in its middle; tapping the open tab again returns to
its top, and pulling a tab down syncs. The breadcrumb's steps are plain
links between "›", the studyset itself bold. A long description is cut at
a fixed height, measured, with Read more opening it whole under the
studyset's title. A studyset that no longer exists leads back to the
library.

The topics: All topics on the primary colour, in view also while they
are rearranged; each topic with the study it invites in a round icon,
what it holds ("Empty" with nothing, files counted too), and its options
(now with Reset progress) behind "…" or a long press where the finger
is; New sub-studyset at the foot below a line, the list with its
scrollbar always shown. All topics opens Add material while nothing is
due.

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

@@ -54,6 +54,7 @@
   "libraryRefresh": "Refresh",
   "libraryRetry": "Retry",
   "studysetNoContent": "No content yet",
+  "studysetEmpty": "Empty",
   "studysetActionReview": "Review",
   "studysetActionStudy": "Study",
   "studysetActionAdd": "Add content",
@@ -250,6 +251,26 @@
   "studysetStudy": "Study",
   "studysetLearnCount": "Learn {count}",
   "@studysetLearnCount": {"placeholders": {"count": {"type": "int"}}},
+  "studysetLearnFlashcards": "{count, plural, =1{Learn 1 flashcard} other{Learn {count} flashcards}}",
+  "@studysetLearnFlashcards": {"placeholders": {"count": {"type": "int"}}},
+  "studysetNothingToStudy": "Nothing to study yet",
+  "studysetStudyMode": "Study mode",
+  "studysetStartPath": "Start: {title}",
+  "@studysetStartPath": {"placeholders": {"title": {"type": "String"}}},
+  "studysetContinuePath": "Continue: {title}",
+  "@studysetContinuePath": {"placeholders": {"title": {"type": "String"}}},
+  "studysetStartPathHint": "Begin the first step of this path.",
+  "studysetContinuePathHint": "Pick up the next path step where you left off.",
+  "studysetSpacedRepetition": "Spaced repetition",
+  "studysetSpacedRepetitionHint": "Review the cards that are due, scheduled by FSRS.",
+  "studysetImportContent": "Import content",
+  "studysetImportPath": "Learning path",
+  "studysetImportPathHint": "From a Halkyon path JSON file",
+  "studysetImportAnki": "Anki deck",
+  "studysetImportAnkiHint": "From an .apkg or .colpkg file",
+  "studysetReorder": "Reorder",
+  "studysetReorderPaths": "Reorder paths",
+  "studysetReorderDone": "Done",
   "studysetOpenTopics": "Show topics",
   "studysetTopics": "Topics",
   "studysetAllTopics": "All topics",
@@ -752,6 +773,7 @@
   "personDataFailed": "Couldn't open this device's data.",
   "sessionUnreachable": "Couldn't reach the server.",
   "notFoundGone": "This no longer exists. It may have been deleted on another device.",
+  "studysetBackToLibrary": "Back to library",
   "fileImage": "Image",
   "fileSound": "Sound",
   "fileImageUnavailable": "This image isn't on this device yet. It shows once it's uploaded and you're online.",