Add analytics page, auth error handling, and period navigation fix

Features
Analytics Page: Full-featured analytics dashboard with KPI cards, cash flow trend chart, net worth progression, spending patterns by day-of-week, top spending categories, and income sources breakdown. Includes PDF export via QuestPDF for selected periods. Implemented on both desktop and mobile (simplified).
Auth Error Handling: Map Supabase GotrueException errors to AuthError enum with user-friendly messages for login and signup. Display errors in sign-in and sign-up panels.
Dynamic Transaction/Account Counts: Replace hardcoded "46 transactions" and "4 accounts" text with FilteredTransactionCount and ActiveAccountCount properties bound to actual data.

Fixes
Budget Period Navigation: Fix year-aware date comparison in CanGoToPreviousPeriod and CanGoToNextPeriod. Previously only compared months, preventing navigation before January of current year.

Changes
AnalyticsViewModel: Period selector, KPI calculations, chart data builders (cash flow, net worth, day-of-week, top categories, income sources), PDF export
PdfExportService: QuestPDF report generation with print-optimized styling
AuthViewModel: Error display with GotrueException mapping
BudgetViewModel: Year-aware period navigation
TransactionsViewModel: FilteredTransactionCount property
AccountsViewModel: ActiveAccountCount property
MainViewModel: Analytics navigation and AnalyticsViewModel integration
Views: Analytics button wired, error messages displayed, count bindings updated

Clario.Desktop/Clario.Desktop.csproj

@@ -22,6 +22,7 @@
         <PackageReference Include="Deadpikle.AvaloniaProgressRing" />
         <PackageReference Include="FluentAvalonia.ProgressRing" />
         <PackageReference Include="LiveChartsCore.SkiaSharpView.Avalonia" />
+        <PackageReference Include="QuestPDF" />
         <PackageReference Include="SkiaSharp.NativeAssets.Linux" />
         <PackageReference Include="SkiaSharp.NativeAssets.WebAssembly" />
         <PackageReference Include="Supabase" />