feat(campaign): implement Event Tent campaign system

Adds the full campaign/event-tent feature:

Packet layer:
- MsgMhfApplyCampaign: Unk0/Unk1/Unk2 → CampaignID/Code (null-terminated 16-byte string)
- MsgMhfAcquireItem: Unk0/Length/Unk1 → RewardIDs []uint32
- MsgMhfEnumerateItem: remove Unk0/Unk1 (RE'd: zeroed + always-2, ignored)
- MsgMhfStateCampaign: Unk1 → NullPadding (RE'd: always zero)
- MsgMhfTransferItem: Unk0/Unk1/Unk2 → QuestID/ItemType/Quantity (RE'd)

Handler layer (handlers_campaign.go):
- handleMsgMhfEnumerateCampaign: reads campaigns, categories, links from DB;
  prefix moved into pascal string slot 3 of each event entry (RE confirmed
  3-section response format — removes spurious intermediate section)
- handleMsgMhfStateCampaign: returns stamp count and redeemable flag
- handleMsgMhfApplyCampaign: validates and records code redemption
- handleMsgMhfEnumerateItem: lists rewards gated by stamp count
- handleMsgMhfAcquireItem: marks rewards as claimed
- handleMsgMhfTransferItem: records campaign quest completion (item_type=9)

Quest gating (handlers_quest.go):
- makeEventQuest: for QuestTypeSpecialTool, check campaign stamp count and
  deadline before allowing the quest (WriteBool true/false)

Database:
- 0010_campaign.sql: 8-table schema (campaigns, categories, links, rewards,
  claimed, state, codes, quest)
- CampaignDemo.sql: community-researched live game campaign data

server/channelserver/handlers_quest.go

@@ -313,7 +313,34 @@ func makeEventQuest(s *Session, eq EventQuest) ([]byte, error) {
 	}
 	bf.WriteUint8(eq.QuestType)
 	if eq.QuestType == QuestTypeSpecialTool {
-		bf.WriteBool(false)
+		var stamps, required int
+		var deadline time.Time
+		err := s.server.db.QueryRow(`SELECT COUNT(*) FROM campaign_state WHERE campaign_id = (
+			SELECT campaign_id
+			FROM campaign_rewards
+			WHERE item_type = 9
+			AND item_id = $1
+			LIMIT 1
+		) AND character_id = $2`, eq.QuestID, s.charID).Scan(&stamps)
+		if err != nil {
+			bf.WriteBool(false)
+		} else {
+			err = s.server.db.QueryRow(`SELECT stamps, end_time
+			FROM campaigns
+			WHERE id = (
+				SELECT campaign_id
+				FROM campaign_rewards
+				WHERE item_type = 9
+				AND item_id = $1
+				LIMIT 1
+			)`, eq.QuestID).Scan(&required, &deadline)
+			required = campaignRequiredStamps(required)
+			if err == nil && stamps >= required && deadline.After(time.Now()) {
+				bf.WriteBool(true)
+			} else {
+				bf.WriteBool(false)
+			}
+		}
 	} else {
 		bf.WriteBool(true)
 	}