Completes Phase 1: Beancount patterns adoption

Implements core improvements from Phase 1 of the Beancount patterns adoption:

- Uses Decimal for fiat amounts to prevent floating point errors
- Adds a meta field to journal entries for a full audit trail
- Adds a flag field to journal entries for transaction status
- Migrates existing account names to a hierarchical format

This commit introduces a database migration to add the `flag` and `meta` columns to the `journal_entries` table. It also includes updates to the models, CRUD operations, and API endpoints to handle the new fields.

models.py

@@ -1,4 +1,5 @@
 from datetime import datetime
+from decimal import Decimal
 from enum import Enum
 from typing import Optional
 
@@ -13,6 +14,14 @@ class AccountType(str, Enum):
     EXPENSE = "expense"
 
 
+class JournalEntryFlag(str, Enum):
+    """Transaction status flags (Beancount-style)"""
+    CLEARED = "*"      # Fully reconciled/confirmed
+    PENDING = "!"      # Not yet confirmed/awaiting approval
+    FLAGGED = "#"      # Needs review/attention
+    VOID = "x"         # Voided/cancelled entry
+
+
 class Account(BaseModel):
     id: str
     name: str
@@ -55,6 +64,8 @@ class JournalEntry(BaseModel):
     created_at: datetime
     reference: Optional[str] = None  # Invoice ID or reference number
     lines: list[EntryLine] = []
+    flag: JournalEntryFlag = JournalEntryFlag.CLEARED  # Transaction status
+    meta: dict = {}  # Metadata: source, tags, links, notes, etc.
 
 
 class CreateJournalEntry(BaseModel):
@@ -62,20 +73,22 @@ class CreateJournalEntry(BaseModel):
     entry_date: Optional[datetime] = None
     reference: Optional[str] = None
     lines: list[CreateEntryLine]
+    flag: JournalEntryFlag = JournalEntryFlag.CLEARED
+    meta: dict = {}
 
 
 class UserBalance(BaseModel):
     user_id: str
     balance: int  # positive = castle owes user, negative = user owes castle
     accounts: list[Account] = []
-    fiat_balances: dict[str, float] = {}  # e.g. {"EUR": 250.0, "USD": 100.0}
+    fiat_balances: dict[str, Decimal] = {}  # e.g. {"EUR": Decimal("250.0"), "USD": Decimal("100.0")}
 
 
 class ExpenseEntry(BaseModel):
     """Helper model for creating expense entries"""
 
     description: str
-    amount: float  # Amount in the specified currency (or satoshis if currency is None)
+    amount: Decimal  # Amount in the specified currency (or satoshis if currency is None)
     expense_account: str  # account name or ID
     is_equity: bool = False  # True = equity contribution, False = liability (castle owes user)
     user_wallet: str
@@ -87,7 +100,7 @@ class ReceivableEntry(BaseModel):
     """Helper model for creating accounts receivable entries"""
 
     description: str
-    amount: float  # Amount in the specified currency (or satoshis if currency is None)
+    amount: Decimal  # Amount in the specified currency (or satoshis if currency is None)
     revenue_account: str  # account name or ID
     user_id: str  # The user_id (not wallet_id) of the user who owes the castle
     reference: Optional[str] = None
@@ -98,7 +111,7 @@ class RevenueEntry(BaseModel):
     """Helper model for creating revenue entries"""
 
     description: str
-    amount: float  # Amount in the specified currency (or satoshis if currency is None)
+    amount: Decimal  # Amount in the specified currency (or satoshis if currency is None)
     revenue_account: str
     payment_method_account: str  # e.g., "Cash", "Bank", "Lightning"
     reference: Optional[str] = None