feat: centralized error notification service (issue #15)

- Create NotificationService with context provider for centralized error/success messaging
- Add NotificationContainer component to render notification stack
- Integrate NotificationProvider into App root
- Refactor BanUnbanForm to use notification service instead of local error state
- Update fetchError utility to optionally use notification callbacks
- Add comprehensive error handling guidelines to Web-Development.md
- Prevent duplicate notifications with deduplication logic
- Support auto-dismiss with configurable TTL per notification type

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docs/Tasks.md

@@ -1,24 +1,3 @@
-## 14) Error boundary granularity is too coarse
-- Where found:
-	- [frontend/src/App.tsx](frontend/src/App.tsx)
-	- [frontend/src/components/ErrorBoundary.tsx](frontend/src/components/ErrorBoundary.tsx)
-- Why this is needed:
-	- Single top boundary causes full app fallback on local component failures.
-- Goal:
-	- Add page-level and section-level boundaries.
-- What to do:
-	- Wrap risky pages/widgets with local boundaries.
-	- Preserve shell/navigation when a section fails.
-- Possible traps and issues:
-	- Too many boundaries can complicate fallback UX consistency.
-- Docs changes needed:
-	- Add frontend resilience/fallback strategy.
-- Doc references:
-	- [Docs/Web-Development.md](Docs/Web-Development.md)
-	- https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary
-
----
-
 ## 15) Fragmented async error UX handling in components
 - Where found:
 	- [frontend/src/pages/jails/BanUnbanForm.tsx](frontend/src/pages/jails/BanUnbanForm.tsx)