feat: Complete Phase 2 with explicit expense states

This commit finalizes Phase 2 by introducing an `ExpenseStatus` enum to formally define the lifecycle of an expense.

- Adds an `ExpenseStatus` enum in `src/data_models.py` with states like `RECEIVED`, `AWAITING_CONFIRMATION`, and `CONFIRMED`.
- Updates the `ProvisionalExpense` and `FinalExpense` models to use the new enum for their `status` fields, improving type safety and clarity.
- Marks all of Phase 2 as complete in `tasks.md`.

src/data_models.py

@@ -1,6 +1,19 @@
 from pydantic import BaseModel, Field
 from typing import Optional, List
 from datetime import datetime, date
+from enum import Enum
+
+
+class ExpenseStatus(str, Enum):
+    """
+    Defines the explicit states an expense can be in throughout its lifecycle.
+    """
+    RECEIVED = "RECEIVED"
+    ANALYZED = "ANALYZED"
+    AWAITING_CONFIRMATION = "AWAITING_CONFIRMATION"
+    CONFIRMED = "CONFIRMED"
+    CORRECTED = "CORRECTED"
+    STORED = "STORED"
 
 class RawInput(BaseModel):
     """
@@ -39,7 +52,7 @@ class ProvisionalExpense(BaseModel):
     confidence_score: float
     processing_method: str = Field(..., description="How the expense was classified, e.g., 'provider_match', 'keyword_match', 'ai_inference'")
     validation_notes: List[str] = []
-    status: str = "AWAITING_CONFIRMATION"
+    status: ExpenseStatus = ExpenseStatus.AWAITING_CONFIRMATION
     timestamp: datetime = Field(default_factory=datetime.now)
 
 class FinalExpense(BaseModel):
@@ -64,4 +77,4 @@ class FinalExpense(BaseModel):
     confirmed_at: datetime = Field(default_factory=datetime.now)
     audit_log: List[str] = []
 
-    status: str = "CONFIRMED"
+    status: ExpenseStatus = ExpenseStatus.CONFIRMED

tasks.md

@@ -36,8 +36,8 @@ Principio rector:
 
 - [x] **2.1 Modelos Pydantic**
   - [x] Crear modelos: `RawInput`, `ExtractedExpense`, `ProvisionalExpense`, `FinalExpense`.
-- [ ] **2.2 Estados del Gasto**
-  - [ ] Definir estados explícitos: `RECEIVED`, `ANALYZED`, `AWAITING_CONFIRMATION`, `CONFIRMED`, `CORRECTED`, `STORED`.
+- [x] **2.2 Estados del Gasto**
+  - [x] Definir estados explícitos: `RECEIVED`, `ANALYZED`, `AWAITING_CONFIRMATION`, `CONFIRMED`, `CORRECTED`, `STORED`.
 
 ---