refactor(channelserver): extract Event, Achievement, Shop, and Cafe repositories

Move 22 raw SQL queries from 4 handler files into dedicated repository
structs, continuing the repository extraction pattern. Achievement
insert uses ON CONFLICT DO NOTHING to eliminate check-then-insert race,
and IncrementScore validates the column index to prevent SQL injection.

server/channelserver/repo_shop.go

@@ -0,0 +1,44 @@
+package channelserver
+
+import (
+	"github.com/jmoiron/sqlx"
+)
+
+// ShopRepository centralizes all database access for shop-related tables.
+type ShopRepository struct {
+	db *sqlx.DB
+}
+
+// NewShopRepository creates a new ShopRepository.
+func NewShopRepository(db *sqlx.DB) *ShopRepository {
+	return &ShopRepository{db: db}
+}
+
+// GetShopItems returns shop items with per-character purchase counts.
+func (r *ShopRepository) GetShopItems(shopType uint8, shopID uint32, charID uint32) (*sqlx.Rows, error) {
+	return r.db.Queryx(`SELECT id, item_id, cost, quantity, min_hr, min_sr, min_gr, store_level, max_quantity,
+       		COALESCE((SELECT bought FROM shop_items_bought WHERE shop_item_id=si.id AND character_id=$3), 0) as used_quantity,
+       		road_floors, road_fatalis FROM shop_items si WHERE shop_type=$1 AND shop_id=$2
+       		`, shopType, shopID, charID)
+}
+
+// RecordPurchase upserts a purchase record, adding to the bought count.
+func (r *ShopRepository) RecordPurchase(charID, shopItemID, quantity uint32) error {
+	_, err := r.db.Exec(`INSERT INTO shop_items_bought (character_id, shop_item_id, bought)
+		VALUES ($1,$2,$3) ON CONFLICT (character_id, shop_item_id)
+		DO UPDATE SET bought = bought + $3
+		WHERE EXCLUDED.character_id=$1 AND EXCLUDED.shop_item_id=$2
+	`, charID, shopItemID, quantity)
+	return err
+}
+
+// GetFpointItem returns the quantity and fpoints cost for a frontier point item.
+func (r *ShopRepository) GetFpointItem(tradeID uint32) (quantity, fpoints int, err error) {
+	err = r.db.QueryRow("SELECT quantity, fpoints FROM fpoint_items WHERE id=$1", tradeID).Scan(&quantity, &fpoints)
+	return
+}
+
+// GetFpointExchangeList returns all frontier point exchange items ordered by buyable status.
+func (r *ShopRepository) GetFpointExchangeList() (*sqlx.Rows, error) {
+	return r.db.Queryx(`SELECT id, item_type, item_id, quantity, fpoints, buyable FROM fpoint_items ORDER BY buyable DESC`)
+}