Major refactor: Split Cards and Accounts into separate tables

Schema Changes:
- Add Account model (Institution, AccountType enum, Last4, Owner, Nickname)
- Add Transfer model for tracking money movement between accounts
- Update Transaction to support both CardId and AccountId (nullable FKs)
- Rename Transaction.CardLast4 → Last4 (works for both cards and accounts)
- Add PaymentMethodLabel computed property to Transaction
- Create EF Core migration: SplitCardsAndAccounts

Data Model Improvements:
- Accounts: Checking, Savings, Other types
- Transfers: Source/Destination accounts, optional link to original transaction
- Transactions can now link to either a Card OR an Account
- Transfer categories excluded from spending reports via TransactionFilters

UI Pages:
- Add Accounts.cshtml - List all bank accounts with transaction counts
- Add EditAccount.cshtml - Create/edit bank accounts
- Add Accounts link to navigation
- Update all references from CardLast4 to Last4

Service Layer Updates:
- Update CardResolutionResult to use nullable CardId and renamed Last4
- Update TransactionKey record to include AccountId
- Update IsDuplicate check to include both CardId and AccountId
- Update all PaymentMethodLabel usage across pages

This architecture allows proper separation of credit cards from bank
accounts and enables tracking of transfers between accounts without
double-counting in spending reports.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.claude/settings.local.json

@@ -2,7 +2,9 @@
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+      "Bash(git commit:*)",
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