Implement friend APIs and target profile support

- Add friend search/list/request/requestCancel/response/expel handlers and schemas
- Store friend relationships in user_friend and backfill default friend links at startup
- Auto-add the default user as a friend for newly created accounts
- Support target user_id in /api profile requests and return target profile data
- Make profile accessory_info optional to avoid zero-value accessory payloads
- Update login topInfo friend counters from friend relationship state

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

internal/handler/friend/request.go

@@ -0,0 +1,103 @@
+package friend
+
+import (
+	"errors"
+	"honoka-chan/internal/middleware"
+	usermodel "honoka-chan/internal/model/user"
+	"honoka-chan/internal/router"
+	friendschema "honoka-chan/internal/schema/friend"
+	"honoka-chan/internal/session"
+	honokautils "honoka-chan/internal/utils"
+
+	"github.com/gin-gonic/gin"
+)
+
+func request(ctx *gin.Context) {
+	ss := session.Get(ctx)
+	defer ss.Finalize()
+
+	req := friendschema.UserIDReq{}
+	err := honokautils.ParseRequestData(ctx, &req)
+	if ss.CheckErr(err) {
+		return
+	}
+
+	targetUserID, err := resolveActualFriendUserID(ss, req.UserID)
+	if ss.CheckErr(err) {
+		return
+	}
+	if targetUserID == ss.UserID {
+		ss.CheckErr(errors.New("cannot add self as friend"))
+		return
+	}
+
+	isFriend, err := areUsersFriends(ss, ss.UserID, targetUserID)
+	if ss.CheckErr(err) {
+		return
+	}
+	if isFriend {
+		ss.Respond(friendschema.RequestResp{
+			ResponseData: friendschema.RequestData{
+				IsFriend: true,
+			},
+			ReleaseInfo: []any{},
+			StatusCode:  200,
+		})
+		return
+	}
+
+	reversePending, err := ss.UserEng.Table(new(usermodel.UserFriend)).
+		Where("user_id = ?", targetUserID).
+		Where("friend_user_id = ?", ss.UserID).
+		Where("status = ?", usermodel.FriendStatusPending).
+		Exist()
+	if ss.CheckErr(err) {
+		return
+	}
+
+	selfAwaitingApproval, err := ss.UserEng.Table(new(usermodel.UserFriend)).
+		Where("user_id = ?", ss.UserID).
+		Where("friend_user_id = ?", targetUserID).
+		Where("status = ?", usermodel.FriendStatusAwaitingApproval).
+		Exist()
+	if ss.CheckErr(err) {
+		return
+	}
+
+	if reversePending && selfAwaitingApproval {
+		err = usermodel.EnsureMutualFriendWithIsNew(ss.UserEng, ss.UserID, targetUserID, usermodel.FriendStatusApproved, true, true)
+		if ss.CheckErr(err) {
+			return
+		}
+
+		ss.Respond(friendschema.RequestResp{
+			ResponseData: friendschema.RequestData{
+				IsFriend: true,
+			},
+			ReleaseInfo: []any{},
+			StatusCode:  200,
+		})
+		return
+	}
+
+	err = usermodel.EnsureFriendLink(ss.UserEng, ss.UserID, targetUserID, usermodel.FriendStatusPending, false)
+	if ss.CheckErr(err) {
+		return
+	}
+	err = usermodel.EnsureFriendLink(ss.UserEng, targetUserID, ss.UserID, usermodel.FriendStatusAwaitingApproval, true)
+	if ss.CheckErr(err) {
+		return
+	}
+
+	ss.Respond(friendschema.RequestResp{
+		ResponseData: friendschema.RequestData{
+			IsFriend: false,
+		},
+		ReleaseInfo: []any{},
+		StatusCode:  200,
+	})
+}
+
+func init() {
+	router.AddHandler("main.php", "POST", "/friend/request", middleware.Common, request)
+}