feat: migrate persistence from JSON to SQLModel (Phase 1)

- Integrated SQLModel with SQLite for robust data persistence
- Refactored UserManager and WatchlistManager to use SQL queries
- Migrated models to SQLModel with relationships and primary keys
- Updated test suite with in-memory database isolation
- Removed deprecated JSON storage files

app/models/auth.py

@@ -1,15 +1,41 @@
-"""Authentication models for user management"""
-from pydantic import BaseModel, EmailStr, Field
-from typing import Optional
+"""Authentication models for user management with SQLModel support"""
+import uuid
+from pydantic import BaseModel, EmailStr, Field as PydanticField
+from typing import Optional, List
 from datetime import datetime
+from sqlmodel import SQLModel, Field, Relationship
 
 
-class UserCreate(BaseModel):
-    """Schema for user registration"""
-    username: str = Field(..., min_length=3, max_length=50)
-    email: Optional[EmailStr] = None
-    password: str = Field(..., min_length=6)
+class UserBase(SQLModel):
+    """Base schema for user data"""
+    username: str = Field(index=True, unique=True, min_length=3, max_length=50)
+    email: Optional[str] = Field(default=None, index=True)
     full_name: Optional[str] = None
+    is_active: bool = Field(default=True)
+
+
+class UserTable(UserBase, table=True):
+    """Database table for users"""
+    __tablename__ = "users"
+    
+    id: str = Field(
+        default_factory=lambda: str(uuid.uuid4()),
+        primary_key=True,
+        index=True,
+        nullable=False
+    )
+    hashed_password: str
+    created_at: datetime = Field(default_factory=datetime.now)
+    last_login: Optional[datetime] = None
+    
+    # Relationships
+    watchlist_items: List["WatchlistItemTable"] = Relationship(back_populates="user")
+
+
+class UserCreate(UserBase):
+    """Schema for user registration"""
+    password: str = PydanticField(..., min_length=6)
+    email: Optional[EmailStr] = None
 
 
 class UserLogin(BaseModel):
@@ -18,13 +44,9 @@ class UserLogin(BaseModel):
     password: str
 
 
-class User(BaseModel):
-    """Schema for user data"""
+class User(UserBase):
+    """Schema for user data (API Response)"""
     id: str
-    username: str
-    email: Optional[str] = None
-    full_name: Optional[str] = None
-    is_active: bool = True
     created_at: datetime
     last_login: Optional[datetime] = None