Implement Phase 6: automated bank sync (Plaid + SimpleFIN) & settings

Add automated transaction syncing via Plaid and SimpleFIN providers,
a Settings page for managing connections and account mappings,
background scheduled syncing, and sync history logging.

New backend: BankSync plugin project with PlaidSyncProvider and
SimpleFinSyncProvider, SyncConnection/LinkedAccount/SyncLog models,
AES-256 encryption service, BankSyncService orchestration,
BankSyncBackgroundService (15-min tick), and BankSyncController
(13 endpoints). EF migration creates sync_connections,
linked_accounts, and sync_logs tables.

New frontend: Settings view with 3 tabs (Profile, Bank Connections,
Sync History), bankSync API service, BankSyncComplete SignalR
notifications, and Settings nav item in sidebar + avatar dropdown.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Purrse.Core/Models/Account.cs

@@ -25,4 +25,5 @@ public class Account
     public ICollection<Transaction> Transactions { get; set; } = new List<Transaction>();
     public ICollection<InvestmentHolding> InvestmentHoldings { get; set; } = new List<InvestmentHolding>();
     public ICollection<Reconciliation> Reconciliations { get; set; } = new List<Reconciliation>();
+    public ICollection<LinkedAccount> LinkedAccounts { get; set; } = new List<LinkedAccount>();
 }

src/Purrse.Core/Models/LinkedAccount.cs

@@ -0,0 +1,19 @@
+namespace Purrse.Core.Models;
+
+public class LinkedAccount
+{
+    public Guid Id { get; set; }
+    public Guid SyncConnectionId { get; set; }
+    public Guid? AccountId { get; set; }
+    public string ExternalAccountId { get; set; } = string.Empty;
+    public string ExternalAccountName { get; set; } = string.Empty;
+    public string? ExternalAccountType { get; set; }
+    public string? ExternalAccountMask { get; set; }
+    public decimal? LastKnownBalance { get; set; }
+    public bool IsEnabled { get; set; } = true;
+    public DateTime? LastSyncAt { get; set; }
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public SyncConnection SyncConnection { get; set; } = null!;
+    public Account? Account { get; set; }
+}

src/Purrse.Core/Models/SyncConnection.cs

@@ -0,0 +1,24 @@
+using Purrse.Core.Enums;
+
+namespace Purrse.Core.Models;
+
+public class SyncConnection
+{
+    public Guid Id { get; set; }
+    public Guid UserId { get; set; }
+    public SyncProvider Provider { get; set; }
+    public string InstitutionName { get; set; } = string.Empty;
+    public string? InstitutionId { get; set; }
+    public string EncryptedAccessToken { get; set; } = string.Empty;
+    public string? PlaidItemId { get; set; }
+    public bool IsActive { get; set; } = true;
+    public int SyncIntervalMinutes { get; set; } = 360;
+    public DateTime? LastSyncAt { get; set; }
+    public string? LastSyncError { get; set; }
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    public User User { get; set; } = null!;
+    public ICollection<LinkedAccount> LinkedAccounts { get; set; } = new List<LinkedAccount>();
+    public ICollection<SyncLog> SyncLogs { get; set; } = new List<SyncLog>();
+}

src/Purrse.Core/Models/SyncLog.cs

@@ -0,0 +1,21 @@
+using Purrse.Core.Enums;
+
+namespace Purrse.Core.Models;
+
+public class SyncLog
+{
+    public Guid Id { get; set; }
+    public Guid SyncConnectionId { get; set; }
+    public Guid? LinkedAccountId { get; set; }
+    public SyncStatus Status { get; set; }
+    public int TransactionsFetched { get; set; }
+    public int TransactionsImported { get; set; }
+    public int TransactionsSkipped { get; set; }
+    public string? ErrorMessage { get; set; }
+    public DateTime StartedAt { get; set; }
+    public DateTime? CompletedAt { get; set; }
+    public TimeSpan? Duration { get; set; }
+
+    public SyncConnection SyncConnection { get; set; } = null!;
+    public LinkedAccount? LinkedAccount { get; set; }
+}

src/Purrse.Core/Models/User.cs

@@ -12,4 +12,5 @@ public class User
     public DateTime? RefreshTokenExpiresAt { get; set; }
 
     public ICollection<Account> Accounts { get; set; } = new List<Account>();
+    public ICollection<SyncConnection> SyncConnections { get; set; } = new List<SyncConnection>();
 }