webui: Make some user preferences configurable

This extends 09f0237560.

- Extend user_pref with configurable profile fields and automatic migration defaults
- Move user info responses to read from user_pref instead of hardcoded values
- Add admin profile page for editing UI values after login

Signed-off-by: Sean Du <do4suki@gmail.com>

internal/handler/api/user/info.go

@@ -1,7 +1,6 @@
 package user
 
 import (
-	usermodel "honoka-chan/internal/model/user"
 	userapischema "honoka-chan/internal/schema/api/user"
 	"honoka-chan/internal/session"
 	"time"
@@ -12,12 +11,6 @@ import (
 func userInfo(ctx *gin.Context) (res any, err error) {
 	ss := session.Get(ctx)
 
-	pref := usermodel.UserPref{}
-	_, err = ss.UserEng.Table("user_pref").Where("user_id = ?", ss.UserID).Get(&pref)
-	if err != nil {
-		return nil, err
-	}
-
 	res = userapischema.InfoResp{
 		Result:     ss.GetUserInfo(),
 		Status:     200,