refactor(channelserver): extract StampRepository, DistributionRepository, and SessionRepository

Eliminate 18 direct s.server.db calls from handlers_items.go,
handlers_distitem.go, and handlers_session.go by moving queries into
dedicated repository types.

New repositories:
- StampRepository (7 methods, stamps table)
- DistributionRepository (4 methods, distribution/distribution_items)
- SessionRepository (4 methods, sign_sessions/servers)

Also adds ClearTreasureHunt and InsertKillLog to GuildRepository,
which already owns those tables for read operations.

server/channelserver/repo_distribution.go

@@ -0,0 +1,79 @@
+package channelserver
+
+import (
+	"github.com/jmoiron/sqlx"
+)
+
+// DistributionRepository centralizes all database access for the distribution,
+// distribution_items, and distributions_accepted tables.
+type DistributionRepository struct {
+	db *sqlx.DB
+}
+
+// NewDistributionRepository creates a new DistributionRepository.
+func NewDistributionRepository(db *sqlx.DB) *DistributionRepository {
+	return &DistributionRepository{db: db}
+}
+
+// List returns all distributions matching the given character and type.
+func (r *DistributionRepository) List(charID uint32, distType uint8) ([]Distribution, error) {
+	rows, err := r.db.Queryx(`
+		SELECT d.id, event_name, description, COALESCE(rights, 0) AS rights, COALESCE(selection, false) AS selection, times_acceptable,
+		COALESCE(min_hr, -1) AS min_hr, COALESCE(max_hr, -1) AS max_hr,
+		COALESCE(min_sr, -1) AS min_sr, COALESCE(max_sr, -1) AS max_sr,
+		COALESCE(min_gr, -1) AS min_gr, COALESCE(max_gr, -1) AS max_gr,
+		(
+    		SELECT count(*) FROM distributions_accepted da
+    		WHERE d.id = da.distribution_id AND da.character_id = $1
+		) AS times_accepted,
+		COALESCE(deadline, TO_TIMESTAMP(0)) AS deadline
+		FROM distribution d
+		WHERE character_id = $1 AND type = $2 OR character_id IS NULL AND type = $2 ORDER BY id DESC
+	`, charID, distType)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var dists []Distribution
+	for rows.Next() {
+		var d Distribution
+		if err := rows.StructScan(&d); err != nil {
+			continue
+		}
+		dists = append(dists, d)
+	}
+	return dists, nil
+}
+
+// GetItems returns all items for a given distribution.
+func (r *DistributionRepository) GetItems(distributionID uint32) ([]DistributionItem, error) {
+	rows, err := r.db.Queryx(`SELECT id, item_type, COALESCE(item_id, 0) AS item_id, COALESCE(quantity, 0) AS quantity FROM distribution_items WHERE distribution_id=$1`, distributionID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var items []DistributionItem
+	for rows.Next() {
+		var item DistributionItem
+		if err := rows.StructScan(&item); err != nil {
+			continue
+		}
+		items = append(items, item)
+	}
+	return items, nil
+}
+
+// RecordAccepted records that a character has accepted a distribution.
+func (r *DistributionRepository) RecordAccepted(distributionID, charID uint32) error {
+	_, err := r.db.Exec(`INSERT INTO public.distributions_accepted VALUES ($1, $2)`, distributionID, charID)
+	return err
+}
+
+// GetDescription returns the description text for a distribution.
+func (r *DistributionRepository) GetDescription(distributionID uint32) (string, error) {
+	var desc string
+	err := r.db.QueryRow("SELECT description FROM distribution WHERE id = $1", distributionID).Scan(&desc)
+	return desc, err
+}