feat(app): tag, edit, delete and swipe cards while studying, with tidier session sheets

- Above every studied card (but a matching one): the PDF it came from,
  its tags on one line ("+2 tags" for the rest) or "Add tags", and a
  menu to tag, edit or delete it; the session follows (an edited card
  shows as saved, a deleted one leaves the round).
- On phones, a front/back or vocabulary card swiped right is rated
  Good, left Bad; it tilts over the colour it heads for, and springs
  back when let go early.
- The session's settings: "Settings", a 48 dp Save that warns mid-round
  ("Heads up!"), steppers in an outlined box ("20 / day", "5 / 50"),
  the order in an outlined dropdown, the chosen tags with the rest
  behind "Filter by tags" / "+3 more".
- A studyset's study options: Save above Reset to defaults, the
  description small, reviews a day in steps of 25.
- One stepper look everywhere (study, Pomodoro profiles), its buttons
  "Decrease" and "Increase".

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

AGENTS.md

@@ -97,7 +97,7 @@ A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS s
 - **Material comes from `package:material_ui`** (Cupertino from `package:cupertino_ui`), never from `package:flutter/material.dart`, which Flutter deprecates from its November 2026 release on. Packages still on the SDK's copy get the app's theme and localizations through `MaterialUiCompatibilityBridge` in `MaterialApp.builder`; remove it once they have moved.
 - **Navigation is `go_router`**: the routes in `lib/src/app/app_router.dart`, their paths in `core/router/route_paths.dart`. Four tabs (Home, Library, Explore, Profile) are the branches of a `StatefulShellRoute`, each keeping its own stack of screens alive while another tab shows (`tabsContainer`, go_router's indexed stack plus `TabVisibility`, which a screen depends on to stop something once its tab is hidden); `AppShell` shows them as a navigation rail from 600 dp on and as a navigation bar below, and choosing the open tab again returns to its first screen. A tab's own screens are routes nested in its branch, reached with `context.go` (a studyset's screen in the library), and a studyset's topic opens on top of it with `context.push` (the same route, keyed by id, so several can stack); the breadcrumb's steps go up with `context.go`, so back then leads further up. What needs the whole window (studying, a card, settings) is a top-level route over the tabs, reached with `context.push`. Explore stays empty until something is shared.
   - **Routes carry ids, never objects.** A screen finds its item in the repository's live list with `FoundById` (`core/widget/`): a spinner until the list arrives, then the item, or a screen saying it no longer exists (deleted on another device, or an old link). A screen that deletes its item closes, and keeps showing the item while it goes. Why: every location can be built from its path alone, and no screen goes on showing something that has gone.
-- **The look is one theme** (`core/theme/`): `appTheme(brightness)` with hand-written light and dark colour schemes around the brand's cobalt and copper; `Theme.of(context).extras` (`ThemeExtras`) for the colours Material has no role for (states, the four FSRS ratings, a starred star); `PaletteColor` for the 20 colours a person can give content. `theme_test.dart` holds text to WCAG AA contrast (4.5:1) on each palette colour and on the dark theme's primary colour and surface. Layouts follow Material 3's window-size classes (`context.windowSize`, `core/layout/`), and running text stays within `readableContentMaxWidth`. Icons are Lucide (`lucide_icons_flutter`), except a starred star, which needs the fill Lucide lacks; the Material icons left in older screens go when those are restyled. Shared widgets are in `core/widget/` (`SectionCard`, `AppLoadingIndicator`, `confirmDestructiveAction`, `FoundById`, `TitleWithKicker`, `ContentCountsLine`, `showUndoSnackBar`, `ScrollHidingFab`, `PaletteColorPicker`, and the sheets below).
+- **The look is one theme** (`core/theme/`): `appTheme(brightness)` with hand-written light and dark colour schemes around the brand's cobalt and copper; `Theme.of(context).extras` (`ThemeExtras`) for the colours Material has no role for (states, the four FSRS ratings, a starred star); `PaletteColor` for the 20 colours a person can give content. `theme_test.dart` holds text to WCAG AA contrast (4.5:1) on each palette colour and on the dark theme's primary colour and surface. Layouts follow Material 3's window-size classes (`context.windowSize`, `core/layout/`), and running text stays within `readableContentMaxWidth`. Icons are Lucide (`lucide_icons_flutter`), except a starred star and the marks of a choice not yet checked (filled box and circle), which need the fill Lucide lacks; the Material icons left in older screens go when those are restyled. Shared widgets are in `core/widget/` (`SectionCard`, `AppLoadingIndicator`, `confirmDestructiveAction`, `FoundById`, `TitleWithKicker`, `ContentCountsLine`, `showUndoSnackBar`, `ScrollHidingFab`, `PaletteColorPicker`, and the sheets below).
 - **Forms and pickers open as sheets**: `showAdaptiveSheet` with a `SheetScaffold` (title and close button on top, the body scrolling with a scrollbar, always shown on the desktop, and Material 3's lines under the title and above the footer while some of the body lies beyond them, the action pinned below) shows a bottom sheet below expanded windows and a dialog from there on. A sheet that asks before discarding changes (a `PopScope`) passes `swipeable: false`: a bottom sheet swiped away closes without asking its `PopScope` (Flutter issue 152120, open with v3.47). A sheet offering an Undo passes `hasSnackBars: true`, so its snack bars show on it rather than behind its barrier. A picker that changes something outside it reports every change as it happens (`onChanged`) rather than as its result, since a sheet swiped away has none.
 - **Text comes from `AppLocalizations`** (Flutter's gen-l10n, `lib/l10n/`): no string a person reads is written into a widget. The app speaks British English, American English and German (informal "du"; the terms of `app_de.arb`, such as Lernset and Karteikarte, stay consistent). `app_en.arb` is the template and holds British English, also the fallback for any language the app doesn't speak; `app_en_US.arb` overrides only what American English spells differently, and `app_en_GB.arb` is empty, there so that Material and dates format the British way. A new message goes into `app_en.arb` and `app_de.arb` together (`test/l10n/arb_files_test.dart` fails otherwise, and checks the placeholders), and into `app_en_US.arb` if its spelling differs. `resolveAppLocale` (`core/l10n/`) picks the language, never by country alone, and both `MaterialApp`s take `appLocalizationsDelegates`, not gen-l10n's list: that brings flutter_localizations' Material texts, which serve only the SDK's Material, so material_ui's widgets would stay English. Errors found in data go up as values the widgets put into words (`PathImportProblem`, `PathImportTexts`), never as English sentences. The editor's own placeholders are replaced by ours (`buildersWithUnknown`), since the editor's texts follow a process-wide locale of their own. The generated `lib/l10n/app_localizations*.dart` are committed and never edited, analysed or formatted by hand. `flutter pub get` writes them anew, so CI fails when they don't match the `.arb` files.