Adds user equity eligibility management

Implements functionality to manage user equity eligibility, allowing admins to grant and revoke access.

Adds database migration, models, CRUD operations, and API endpoints for managing user equity status.
This feature enables finer-grained control over who can convert expenses to equity contributions.
Validates a user's eligibility before allowing them to submit expenses as equity.

models.py

@@ -247,3 +247,29 @@ class CreateBalanceAssertion(BaseModel):
     fiat_currency: Optional[str] = None
     tolerance_sats: int = 0
     tolerance_fiat: Decimal = Decimal("0")
+
+
+class UserEquityStatus(BaseModel):
+    """Tracks user's equity eligibility and status"""
+    user_id: str  # User's wallet ID
+    is_equity_eligible: bool  # Can user convert expenses to equity?
+    equity_account_name: Optional[str] = None  # e.g., "Equity:Alice"
+    notes: Optional[str] = None  # Admin notes
+    granted_by: str  # Admin who granted eligibility
+    granted_at: datetime
+    revoked_at: Optional[datetime] = None  # If eligibility was revoked
+
+
+class CreateUserEquityStatus(BaseModel):
+    """Create or update user equity eligibility"""
+    user_id: str
+    is_equity_eligible: bool
+    equity_account_name: Optional[str] = None
+    notes: Optional[str] = None
+
+
+class UserInfo(BaseModel):
+    """User information including equity eligibility"""
+    user_id: str
+    is_equity_eligible: bool
+    equity_account_name: Optional[str] = None