feat: a round in the order cards come, shared daily limits, and a start screen

Studying:
- A round is one list in the order its cards come: those done, the one
  shown, those to come. A card due again within the day goes back in
  after 4 more cards when rated Bad, at the end otherwise, so the pills
  above the card follow it; the buttons say "in 4 cards", "at the end",
  "now" (round_order.dart).
- The studied studyset's daily limits hold for everything inside it
  together, as Anki's do for subdecks: twenty topics start 20 new cards
  a day in all, not 20 each.
- The study header's studyset name shows whole on hover or long press.
- The assistant's button sits at the lower left: in the Library across
  from Create studyset, in a studyset above its bar, and higher while
  studying, above the buttons that answer the card.

A studyset:
- Progress also counts the learning paths' steps done and lists the
  PDFs not read to their end, begun first, each opening the reader,
  across its topics (MaterialProgressCubit).
- Next up starts with studying for the exam while one is ahead: its
  reviews due and the new cards its pace leaves for the day.
- Learning paths tagged with a level count towards its automatic exam
  plan and offer it, as cards do.
- A step's first heading equal to its title is dropped on import and
  hidden in paths imported before.

Signing out, or a session the server ended, leads to a start screen
(GitHub, email, without an account, another instance) rather than a new
anonymous account; only the very first start makes one by itself.
Settings names the kind of account and its instance.

Also: the Watch screen reads the cards once for held words and their
progress; its ±10 s buttons tick as the navigation bar does; a map card
keeps its view as its caption changes and brings a picked region
towards the middle; an empty or failed library can be pulled to sync.

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

@@ -648,6 +648,12 @@
   "settingsTitle": "Settings",
   "settingsAccount": "Account",
   "instanceWelcome": "Welcome to Halkyon Learn",
+  "startSignedOut": "Signed out",
+  "startOn": "Start on {instance}:",
+  "@startOn": {"placeholders": {"instance": {"type": "String"}}},
+  "startWithoutAccount": "Start without an account",
+  "startNoGitHubAccount": "No account here signs in with this GitHub account yet. Start without an account, then add GitHub in Profile.",
+  "startOtherInstance": "Use another instance",
   "instanceFirstStartSubtitle": "Choose the instance to keep your studysets on. Someone runs each one; you can add others later.",
   "instanceAddress": "Instance address",
   "instanceUseBuiltIn": "Use {name}",
@@ -660,6 +666,12 @@
   "instanceOpenFailed": "Couldn't open the app on {name}.",
   "@instanceOpenFailed": {"placeholders": {"name": {"type": "String"}}},
   "settingsSwitchAccount": "Switch account",
+  "settingsAccountAnonymous": "Anonymous on {instance}",
+  "@settingsAccountAnonymous": {"placeholders": {"instance": {"type": "String"}}},
+  "settingsAccountSignedIn": "Signed in on {instance}",
+  "@settingsAccountSignedIn": {"placeholders": {"instance": {"type": "String"}}},
+  "accountAnonymous": "Anonymous",
+  "accountSignedIn": "Signed in",
   "accountsTitle": "Accounts",
   "accountAdd": "Add account",
   "accountAddSubtitle": "Choose the instance for the account to add.",
@@ -1100,6 +1112,10 @@
   "studyBackFirstOff": "Show the back of cards first",
   "studyShowAnswer": "Show answer",
   "studyCheck": "Check",
+  "studyComesBackIn": "{count, plural, =1{in 1 card} other{in {count} cards}}",
+  "@studyComesBackIn": {"placeholders": {"count": {"type": "int"}}},
+  "studyComesBackAtEnd": "at the end",
+  "studyComesBackNow": "now",
   "studySelectAll": "Select all that apply",
   "studySelectOne": "Select the correct answer",
   "studyMatchingInstructions": "DRAG AND DROP ONTO CARDS ABOVE",
@@ -2231,12 +2247,27 @@
   "@progressMinutes": {"placeholders": {"minutes": {"type": "int"}}},
   "progressHoursMinutes": "{hours} h {minutes} min",
   "@progressHoursMinutes": {"placeholders": {"hours": {"type": "int"}, "minutes": {"type": "int"}}},
+  "progressPathsInfo": "The steps of this studyset's learning paths, and its topics', that you have done.",
+  "progressStepsDone": "{total, plural, =1{of 1 step done} other{of {total} steps done}}",
+  "@progressStepsDone": {"placeholders": {"total": {"type": "int"}}},
+  "progressReading": "Reading",
+  "progressReadingInfo": "The PDFs of this studyset and its topics not read to their last page yet. Tap one to read on.",
+  "progressPdfPage": "Page {page} of {count}",
+  "@progressPdfPage": {"placeholders": {"page": {"type": "int"}, "count": {"type": "int"}}},
+  "progressPdfNotBegun": "Not begun yet",
+  "progressPdfsAllRead": "{count, plural, =1{The PDF is read to its end.} other{All {count} PDFs are read to their end.}}",
+  "@progressPdfsAllRead": {"placeholders": {"count": {"type": "int"}}},
+  "progressShowAllPdfs": "Show all {count}",
+  "@progressShowAllPdfs": {"placeholders": {"count": {"type": "int"}}},
+  "progressShowFewerPdfs": "Show fewer",
   "planPathsDone": "{count, plural, =1{{done} of 1 path finished} other{{done} of {count} paths finished}}",
   "@planPathsDone": {"placeholders": {"done": {"type": "int"}, "count": {"type": "int"}}},
   "planNoPaths": "No learning paths yet",
   "planNextUp": "Next up",
   "planReview": "{count, plural, =1{Study 1 flashcard} other{Study {count} flashcards}}",
   "@planReview": {"placeholders": {"count": {"type": "int"}}},
+  "planStudyForExam": "{count, plural, =1{Study 1 flashcard for {exam}} other{Study {count} flashcards for {exam}}}",
+  "@planStudyForExam": {"placeholders": {"count": {"type": "int"}, "exam": {"type": "String"}}},
   "planContinue": "Continue “{title}”",
   "@planContinue": {"placeholders": {"title": {"type": "String"}}},
   "planStart": "Start “{title}”",