feat: enhance Mini App design guidelines and refactor layout components

- Updated Mini App design guidelines to include detailed instructions on UI changes, accessibility rules, and verification processes.
- Refactored multiple components to utilize `MiniAppScreen` and `MiniAppScreenContent` for consistent layout structure across the application.
- Improved error handling in `GlobalError` and `NotFound` components by integrating new layout components for better user experience.
- Introduced new hooks for admin functionality, streamlining access checks and data loading processes.
- Enhanced documentation to reflect changes in design policies and component usage, ensuring clarity for future development.

docs/webapp-next-refactor-audit.md

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+# Webapp-next Refactor Baseline Audit
+
+This note captures the baseline before the phased refactor. It defines current risks,
+duplication hotspots, and expected behavior that must not regress.
+
+## 1) Screens and boundaries
+
+- Home route orchestration: `webapp-next/src/app/page.tsx`
+  - Chooses among `AccessDeniedScreen`, `CurrentDutyView`, `CalendarPage`.
+  - Controls app visibility via `appContentReady`.
+- Admin route orchestration: `webapp-next/src/app/admin/page.tsx`
+  - Thin route, but still owns shell duplication and content-ready signaling.
+- Calendar composition root: `webapp-next/src/components/CalendarPage.tsx`
+  - Combines sticky layout, swipe, month loading, auto-refresh, settings button.
+- Current duty feature root: `webapp-next/src/components/current-duty/CurrentDutyView.tsx`
+  - Combines data loading, error/access states, back button, and close action.
+- Admin feature state root: `webapp-next/src/components/admin/useAdminPage.ts`
+  - Combines SDK button handling, admin access, users/duties loading, sheet state,
+    mutation and infinite scroll concerns.
+
+## 2) Telegram integration touchpoints
+
+- SDK/provider bootstrap:
+  - `webapp-next/src/components/providers/TelegramProvider.tsx`
+  - `webapp-next/src/components/ReadyGate.tsx`
+  - `webapp-next/src/lib/telegram-ready.ts`
+- Direct control usage in feature code:
+  - `backButton` in `CurrentDutyView` and `useAdminPage`
+  - `settingsButton` in `CalendarPage`
+  - `closeMiniApp` in `CurrentDutyView`
+- Haptics in feature-level handlers:
+  - `webapp-next/src/lib/telegram-haptic.ts`
+
+Risk: platform behavior is spread across feature components instead of a narrow
+platform boundary.
+
+## 3) Layout and shell duplication
+
+Repeated outer wrappers appear across route and state screens:
+- `content-safe min-h-[var(--tg-viewport-stable-height,100vh)] bg-background`
+- `mx-auto flex w-full max-w-[var(--max-width-app)] flex-col`
+
+Known locations:
+- `webapp-next/src/app/page.tsx`
+- `webapp-next/src/app/admin/page.tsx`
+- `webapp-next/src/components/CalendarPage.tsx`
+- `webapp-next/src/components/states/FullScreenStateShell.tsx`
+- `webapp-next/src/app/not-found.tsx`
+- `webapp-next/src/app/global-error.tsx`
+
+Risk: future safe-area or viewport fixes require multi-file edits.
+
+## 4) Readiness and lifecycle coupling
+
+`appContentReady` is set by multiple screens/routes:
+- `page.tsx`
+- `admin/page.tsx`
+- `CalendarPage.tsx`
+- `CurrentDutyView.tsx`
+
+`ReadyGate` is route-agnostic, but signaling is currently ad hoc.
+Risk: race conditions or deadlock-like "hidden app" scenarios when screen states
+change in future refactors.
+
+## 5) Async/data-loading duplication
+
+Repeated manual patterns (abort, retries, state machine):
+- `webapp-next/src/hooks/use-month-data.ts`
+- `webapp-next/src/components/current-duty/CurrentDutyView.tsx`
+- `webapp-next/src/components/admin/useAdminPage.ts`
+
+Risk: inconsistent retry/access-denied behavior and difficult maintenance.
+
+## 6) Store mixing concerns
+
+`webapp-next/src/store/app-store.ts` currently mixes:
+- session/platform concerns (`lang`, `appContentReady`, `isAdmin`)
+- calendar/domain concerns (`currentMonth`, `pendingMonth`, duties/events)
+- view concerns (`currentView`, `selectedDay`, `error`, `accessDenied`)
+
+Risk: high coupling and larger blast radius for otherwise local changes.
+
+## 7) i18n/a11y gaps to close
+
+- Hardcoded grid label in `CalendarGrid`: `aria-label="Calendar"`.
+- Hardcoded sr-only close text in shared `Sheet`: `"Close"`.
+- Mixed language access strategy (`useTranslation()` vs `getLang()/translate()`),
+  valid for bootstrap/error boundary, but not explicitly codified in one place.
+
+## 8) Telegram Mini Apps compliance checklist (baseline)
+
+Already implemented well:
+- Dynamic theme + runtime sync.
+- Safe-area/content-safe-area usage via CSS vars and layout classes.
+- `ready()` gate and Telegram loader handoff.
+- Android low-performance class handling.
+
+Needs explicit policy/consistency:
+- Vertical swipes policy for gesture-heavy screens.
+- Closing confirmation policy for stateful admin flows.
+- Main/Secondary button usage policy for primary actions.
+- Terminology alignment with current official docs:
+  `safeAreaInset`, `contentSafeAreaInset`, fullscreen events.
+
+## 9) Expected behavior (non-regression)
+
+- `/`:
+  - Shows access denied screen if not allowed.
+  - Opens current-duty view for `startParam=duty`.
+  - Otherwise opens calendar.
+- `/admin`:
+  - Denies non-admin users.
+  - Loads users and duties for selected admin month.
+  - Allows reassignment with visible feedback.
+- Error/fallback states:
+  - `not-found` and global error remain full-screen and theme-safe.
+- Telegram UX:
+  - Back/settings controls remain functional in Telegram context.
+  - Ready handoff happens when first useful screen is visible.