fix: add SQLite compatibility for Decimal types

SQLite doesn't support Decimal natively - it stores DECIMAL columns as
REAL (float). This caused sqlite3.ProgrammingError when writing Decimal
values.

Changes:
- Add prepare_for_db() helper to convert Decimal→float before writes
- Add Pydantic validators to convert float→Decimal on model creation
- Update CRUD layer tests to verify float params for SQLite
- Add SQLite round-trip tests to verify precision is preserved

The data flow is now:
Decimal (calculations) → float (prepare_for_db) → SQLite → float → Decimal (validators)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models.py

@@ -7,6 +7,16 @@ from typing import Optional
 from pydantic import BaseModel, validator
 
 
+def _to_decimal(v):
+    """Convert a value to Decimal, handling floats from database."""
+    if v is None:
+        return None
+    if isinstance(v, Decimal):
+        return v
+    # Convert via string to avoid float precision issues
+    return Decimal(str(v))
+
+
 # DCA Client Models
 class CreateDcaClientData(BaseModel):
     user_id: str
@@ -27,6 +37,10 @@ class DcaClient(BaseModel):
     created_at: datetime
     updated_at: datetime
 
+    @validator('fixed_mode_daily_limit', pre=True)
+    def convert_fixed_mode_daily_limit(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}
 
@@ -65,6 +79,10 @@ class DcaDeposit(BaseModel):
     created_at: datetime
     confirmed_at: Optional[datetime]
 
+    @validator('amount', pre=True)
+    def convert_amount(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}
 
@@ -99,6 +117,10 @@ class DcaPayment(BaseModel):
     created_at: datetime
     transaction_time: Optional[datetime] = None  # Original ATM transaction time
 
+    @validator('amount_fiat', 'exchange_rate', pre=True)
+    def convert_decimals(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}
 
@@ -111,6 +133,10 @@ class ClientBalanceSummary(BaseModel):
     remaining_balance: Decimal  # Available balance for DCA in GTQ
     currency: str
 
+    @validator('total_deposits', 'total_payments', 'remaining_balance', pre=True)
+    def convert_decimals(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}
 
@@ -165,6 +191,13 @@ class StoredLamassuTransaction(BaseModel):
     clients_count: int  # Number of clients who received distributions
     distributions_total_sats: int  # Total sats distributed to clients
 
+    @validator(
+        'fiat_amount', 'commission_percentage', 'discount',
+        'effective_commission', 'exchange_rate', pre=True
+    )
+    def convert_decimals(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}
 
@@ -228,6 +261,10 @@ class LamassuConfig(BaseModel):
     # DCA Client Limits
     max_daily_limit_gtq: Decimal = Decimal("2000")  # Maximum daily limit for Fixed mode clients
 
+    @validator('max_daily_limit_gtq', pre=True)
+    def convert_max_daily_limit(cls, v):
+        return _to_decimal(v)
+
     class Config:
         json_encoders = {Decimal: lambda v: float(v)}