feat: implement JWT authentication system

- Add register endpoint with bcrypt password hashing
- Add login endpoint returning JWT tokens
- Add logout endpoint with token blacklisting
- Add /me endpoint for current user info
- Add rate limiting (5/minute) for login attempts using slowapi
- Add user settings GET and PATCH endpoints
- Create auth middleware via get_current_user dependency
- Add UserSettings and UserSettingsUpdate schemas

src/backend/app/db/schemas.py

@@ -23,6 +23,15 @@ class Token(BaseModel):
     token_type: str
 
 
+class UserSettings(BaseModel):
+    email: EmailStr
+
+
+class UserSettingsUpdate(BaseModel):
+    email: Optional[EmailStr] = None
+    password: Optional[str] = None
+
+
 class BotCreate(BaseModel):
     name: str
     description: Optional[str] = None