feat(channelserver): add daily noon resets for gacha stepup and guild RP

Gacha stepup progress now resets when queried after the most recent
noon boundary, using a new created_at column on gacha_stepup.

Guild member rp_today rolls into rp_yesterday lazily when members are
enumerated after noon, using a new rp_reset_at column on guilds.

Both follow the established lazy-reset pattern from the cafe handler.

server/channelserver/guild_model.go

@@ -56,6 +56,7 @@ type Guild struct {
 	Souls         uint32        `db:"souls"`
 	AllianceID    uint32        `db:"alliance_id"`
 	Icon          *GuildIcon    `db:"icon"`
+	RPResetAt     time.Time     `db:"rp_reset_at"`
 
 	GuildLeader
 }