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/migrations/sql/0010_campaign.sql

@@ -0,0 +1,69 @@
+BEGIN;
+
+CREATE TABLE IF NOT EXISTS public.campaigns (
+  id INTEGER PRIMARY KEY,
+  min_hr INTEGER,
+  max_hr INTEGER,
+  min_sr INTEGER,
+  max_sr INTEGER,
+  min_gr INTEGER,
+  max_gr INTEGER,
+  reward_type INTEGER,
+  stamps INTEGER,
+  receive_type INTEGER,
+  background_id INTEGER,
+  start_time TIMESTAMP WITH TIME ZONE,
+  end_time TIMESTAMP WITH TIME ZONE,
+  title TEXT,
+  reward TEXT,
+  link TEXT,
+  code_prefix TEXT
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_categories (
+  id SERIAL PRIMARY KEY,
+  type INTEGER,
+  title TEXT,
+  description TEXT
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_category_links (
+  id SERIAL PRIMARY KEY,
+  campaign_id INTEGER REFERENCES public.campaigns(id) ON DELETE CASCADE,
+  category_id INTEGER REFERENCES public.campaign_categories(id) ON DELETE CASCADE
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_rewards (
+  id SERIAL PRIMARY KEY,
+  campaign_id INTEGER REFERENCES public.campaigns(id) ON DELETE CASCADE,
+  item_type INTEGER,
+  quantity INTEGER,
+  item_id INTEGER
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_rewards_claimed (
+  character_id INTEGER REFERENCES public.characters(id) ON DELETE CASCADE,
+  reward_id INTEGER REFERENCES public.campaign_rewards(id) ON DELETE CASCADE,
+  PRIMARY KEY (character_id, reward_id)
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_state (
+  id SERIAL PRIMARY KEY,
+  campaign_id INTEGER REFERENCES public.campaigns(id) ON DELETE CASCADE,
+  character_id INTEGER REFERENCES public.characters(id) ON DELETE CASCADE,
+  code TEXT
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_codes (
+  code TEXT PRIMARY KEY,
+  campaign_id INTEGER REFERENCES public.campaigns(id) ON DELETE CASCADE,
+  multi BOOLEAN NOT NULL DEFAULT FALSE
+);
+
+CREATE TABLE IF NOT EXISTS public.campaign_quest (
+  campaign_id INTEGER REFERENCES public.campaigns(id) ON DELETE CASCADE,
+  character_id INTEGER REFERENCES public.characters(id) ON DELETE CASCADE,
+  PRIMARY KEY (campaign_id, character_id)
+);
+
+END;