webui: Add user birthday settings

- Store birth month and day in user_pref with default 10/18
- Migrate existing user_pref rows to fill missing birthday fields
- Expose birthday editing in the webui profile page
- Replace hardcoded birthday values in user info, top info, and product list responses
- Fix birthday month/day field alignment in the profile form

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

internal/handler/api/user/info.go

@@ -2,6 +2,7 @@ package user
 
 import (
 	userapischema "honoka-chan/internal/schema/api/user"
+	userschema "honoka-chan/internal/schema/user"
 	"honoka-chan/internal/session"
 	"time"
 
@@ -12,7 +13,13 @@ func userInfo(ctx *gin.Context) (res any, err error) {
 	ss := session.Get(ctx)
 
 	res = userapischema.InfoResp{
-		Result:     ss.GetUserInfo(),
+		Result: userschema.UserInfoData{
+			User: ss.GetUserInfo(),
+			Birth: userschema.Birth{
+				BirthMonth: ss.UserPref.EffectiveBirthMonth(),
+				BirthDay:   ss.UserPref.EffectiveBirthDay(),
+			},
+		},
 		Status:     200,
 		CommandNum: false,
 		TimeStamp:  time.Now().Unix(),