Add first and last name fields for users

This commit introduces optional `first_name` and `last_name` fields to the user model, including database migrations, backend, and frontend support. It enhances user profiles, updates user creation and editing flows, and refines the UI to display full names where available.

backend/app/schemas/user.py

@@ -5,6 +5,8 @@ from pydantic import BaseModel, EmailStr, field_validator
 class UserOut(BaseModel):
     id: int
     email: EmailStr
+    first_name: str | None = None
+    last_name: str | None = None
     role: str
     created_at: datetime
 
@@ -13,12 +15,16 @@ class UserOut(BaseModel):
 
 class UserCreate(BaseModel):
     email: EmailStr
+    first_name: str | None = None
+    last_name: str | None = None
     password: str
     role: str = "viewer"
 
 
 class UserUpdate(BaseModel):
     email: EmailStr | None = None
+    first_name: str | None = None
+    last_name: str | None = None
     password: str | None = None
     role: str | None = None