refactor(channelserver): eliminate *sqlx.Rows/*sql.Rows from repository interfaces

Move scan loops from handlers into repository methods so that interfaces
return typed slices instead of leaking database cursors. This fixes
resource leaks (7 of 12 call sites never closed rows) and makes all
12 methods mockable for unit tests.

Affected repos: CafeRepo, ShopRepo, EventRepo, RengokuRepo, DivaRepo,
ScenarioRepo, MiscRepo, MercenaryRepo. New structs: DivaEvent,
MercenaryLoan, GuildHuntCatUsage. EventRepo.GetEventQuests left as-is
(requires broader Server refactor).

server/channelserver/repo_scenario.go

@@ -1,6 +1,8 @@
 package channelserver
 
 import (
+	"fmt"
+
 	"github.com/jmoiron/sqlx"
 )
 
@@ -15,6 +17,19 @@ func NewScenarioRepository(db *sqlx.DB) *ScenarioRepository {
 }
 
 // GetCounters returns all scenario counters.
-func (r *ScenarioRepository) GetCounters() (*sqlx.Rows, error) {
-	return r.db.Queryx("SELECT scenario_id, category_id FROM scenario_counter")
+func (r *ScenarioRepository) GetCounters() ([]Scenario, error) {
+	rows, err := r.db.Query("SELECT scenario_id, category_id FROM scenario_counter")
+	if err != nil {
+		return nil, fmt.Errorf("query scenario_counter: %w", err)
+	}
+	defer rows.Close()
+	var result []Scenario
+	for rows.Next() {
+		var s Scenario
+		if err := rows.Scan(&s.MainID, &s.CategoryID); err != nil {
+			return nil, fmt.Errorf("scan scenario_counter: %w", err)
+		}
+		result = append(result, s)
+	}
+	return result, rows.Err()
 }